Redo ILVerfificaiton (#90418)

* Now checks all assemblies in the output directory rather than just `test.exe`
* Once again respects the the ability to skip verifying a single assembly via `[SkipIlVerify("foo.dll")]`
* Now loads core libraries from the output directory (if they exist) instead of from the runtime install dir.
* ALC logic was removed.  I do not understand what value this provided.
* The class libraries lead to a lot of errors.  Rather than having to filter out a large number of errors, I added diff'ing.  ILVerify will check the input assembly and remove any errors that existed in the input assembly.  This makes verifying class libraries viable.  Without it, you'd have to use `[SkipIlverify]` on every core link test or filter out a lot of `VerifierError` values.
* Moved IL verification back to `InitialChecking` where `PeVerifier` was
* Add a test to verify that il verification is mostly working.  It doesn't give complete coverage over every behavior, but it's better than nothing.
* `SkipPeVerify` renamed to `SkipIlVerify`
* `SkipPeVerifyForToolchian` was removed.  There is only 1 tool now.
* Removed `PeVerifier`.
* Remove many [SkipIlVerify] attributes.  Diffing means they are no longer needed
* `ValidateTypeRefsHaveValidAssemblyRefs` now runs regardless of whether or not the IL is verified.  It wasn't clear to me why this logic would only be useful when il was verified.
* Change `UninitializedLocals` to use `ExpectIlFailure`.  This test seems to expect invalid il.  Might as well assert that rather than skip ilverify entirely.
* Remove the logic that disables ilverify when a test uses the unsafe argument.  Diffing makes this obsolete.

* IL Verification errors have been greatly improved.
** will now output all IL errors in the failure message rather than just the first invalid IL.
** Type and Method names are now displayed in the error message.  I didn't do an exhaustive implementation, SRM is so tedious to use, but it's better than not having it
** Tokens and Offsets are formatted nicely

* Extension points opened up for Unity.
** We need to supply different search directories.
** We need to search for `.winmd` files since we support windows runtime.
** In general I opened some things up in case we need to call them

Author: mrvoorhe

src/coreclr/tools/aot/Mono.Linker.Tests/TestCasesRunner/ResultChecker.cs

@@ -45,22 +45,6 @@ public ResultChecker (BaseAssemblyResolver originalsResolver,
 			_linkedReaderParameters = linkedReaderParameters;
 		}
 
-		private static bool ShouldValidateIL (AssemblyDefinition inputAssembly)
-		{
-			if (HasAttribute (inputAssembly, nameof (SkipPeVerifyAttribute)))
-				return false;
-
-			var caaIsUnsafeFlag = (CustomAttributeArgument caa) =>
-				(caa.Type.Name == "String" && caa.Type.Namespace == "System")
-				&& (string) caa.Value == "/unsafe";
-			var customAttributeHasUnsafeFlag = (CustomAttribute ca) => ca.ConstructorArguments.Any (caaIsUnsafeFlag);
-			if (GetCustomAttributes (inputAssembly, nameof (SetupCompileArgumentAttribute))
-				.Any (customAttributeHasUnsafeFlag))
-				return false;
-
-			return true;
-		}
-
 		public virtual void Check (ILCompilerTestCaseResult testResult)
 		{
 			InitializeResolvers (testResult);

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/generated/ILLink.RoslynAnalyzer.Tests.Generator/ILLink.RoslynAnalyzer.Tests.TestCaseGenerator/TestFrameworkTests.g.cs

@@ -75,6 +75,12 @@ public Task CanVerifyInterfacesOnTypesInAssembly ()
 			return RunTest (allowMissingWarnings: true);
 		}
 
+		[Fact]
+		public Task ILVerificationWorks ()
+		{
+			return RunTest (allowMissingWarnings: true);
+		}
+
 		[Fact]
 		public Task VerifyAttributesInAssemblyWorks ()
 		{

src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Assertions/DisableILVerifyDiffingAttribute.cs

@@ -0,0 +1,17 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Mono.Linker.Tests.Cases.Expectations.Assertions;
+
+/// <summary>
+/// This attribute is used to disable removing il verification errors that appear in the input assembly from the output verification results.
+///
+/// The original motivation for this is to make it easier to write a test that mostly verifies that the test frameworks ability to check il is working
+/// correctly.
+/// </summary>
+[AttributeUsage (AttributeTargets.Class)]
+public class DisableILVerifyDiffingAttribute : BaseExpectedLinkedBehaviorAttribute
+{
+}

src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Assertions/ExpectILFailureAttribute.cs

@@ -0,0 +1,14 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+
+namespace Mono.Linker.Tests.Cases.Expectations.Assertions;
+
+[AttributeUsage (AttributeTargets.Class, AllowMultiple = true)]
+public class ExpectILFailureAttribute : BaseExpectedLinkedBehaviorAttribute
+{
+	public ExpectILFailureAttribute (params string[] messageContains)
+	{
+	}
+}

src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Assertions/SkipPeVerifyAttribute.cs renamed to src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Assertions/SkipILVerifyAttribute.cs

@@ -5,24 +5,14 @@
 
 namespace Mono.Linker.Tests.Cases.Expectations.Assertions
 {
-
-	public enum SkipPeVerifyForToolchian
-	{
-		Pedump
-	}
-
 	[AttributeUsage (AttributeTargets.Class, AllowMultiple = true)]
-	public class SkipPeVerifyAttribute : BaseExpectedLinkedBehaviorAttribute
+	public class SkipILVerifyAttribute : BaseExpectedLinkedBehaviorAttribute
 	{
-		public SkipPeVerifyAttribute ()
-		{
-		}
-
-		public SkipPeVerifyAttribute (SkipPeVerifyForToolchian toolchain)
+		public SkipILVerifyAttribute ()
 		{
 		}
 
-		public SkipPeVerifyAttribute (string assemblyName)
+		public SkipILVerifyAttribute (string assemblyName)
 		{
 		}
 	}

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes.Debugger/KeepDebugMembers/DebuggerDisplayAttributeOnAssemblyUsingTarget.cs

@@ -14,9 +14,6 @@ namespace Mono.Linker.Tests.Cases.Attributes.Debugger.KeepDebugMembers
 	[SetupLinkerKeepDebugMembers ("true")]
 #endif
 
-	// Can be removed once this bug is fixed https://bugzilla.xamarin.com/show_bug.cgi?id=58168
-	[SkipPeVerify (SkipPeVerifyForToolchian.Pedump)]
-
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), ".ctor(System.String)")]
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), "set_Target(System.Type)")]
 	public class DebuggerDisplayAttributeOnAssemblyUsingTarget

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes.Debugger/KeepDebugMembers/DebuggerDisplayAttributeOnAssemblyUsingTargetOnUnusedType.cs

@@ -9,10 +9,6 @@
 namespace Mono.Linker.Tests.Cases.Attributes.Debugger.KeepDebugMembers
 {
 	[SetupLinkerTrimMode ("link")]
-
-	// Can be removed once this bug is fixed https://bugzilla.xamarin.com/show_bug.cgi?id=58168
-	[SkipPeVerify (SkipPeVerifyForToolchian.Pedump)]
-
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), ".ctor(System.String)")]
 	public class DebuggerDisplayAttributeOnAssemblyUsingTargetOnUnusedType
 	{

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes.Debugger/KeepDebugMembers/DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameInOtherAssembly.cs

@@ -13,9 +13,6 @@ namespace Mono.Linker.Tests.Cases.Attributes.Debugger.KeepDebugMembers
 	[SetupLinkerTrimMode ("link")]
 	[SetupCompileBefore ("library.dll", new[] { "../Dependencies/DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameInOtherAssembly_Lib.cs" })]
 
-	// Can be removed once this bug is fixed https://bugzilla.xamarin.com/show_bug.cgi?id=58168
-	[SkipPeVerify (SkipPeVerifyForToolchian.Pedump)]
-
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), ".ctor(System.String)")]
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), "set_TargetTypeName(System.String)")]
 

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes.Debugger/KeepDebugMembers/DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameInSameAssembly.cs

@@ -13,9 +13,6 @@ namespace Mono.Linker.Tests.Cases.Attributes.Debugger.KeepDebugMembers
 	[SetupLinkerKeepDebugMembers ("true")]
 #endif
 
-	// Can be removed once this bug is fixed https://bugzilla.xamarin.com/show_bug.cgi?id=58168
-	[SkipPeVerify (SkipPeVerifyForToolchian.Pedump)]
-
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), ".ctor(System.String)")]
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), "set_TargetTypeName(System.String)")]
 	public class DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameInSameAssembly

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes.Debugger/KeepDebugMembers/DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameOfGenericTypeInOtherAssembly.cs

@@ -15,9 +15,6 @@ namespace Mono.Linker.Tests.Cases.Attributes.Debugger.KeepDebugMembers
 #endif
 	[SetupCompileBefore ("library.dll", new[] { "../Dependencies/DebuggerDisplayAttributeOnAssemblyUsingTargetTypeNameInOtherAssembly_Lib.cs" })]
 
-	// Can be removed once this bug is fixed https://bugzilla.xamarin.com/show_bug.cgi?id=58168
-	[SkipPeVerify (SkipPeVerifyForToolchian.Pedump)]
-
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), ".ctor(System.String)")]
 	[KeptMemberInAssembly (PlatformAssemblies.CoreLib, typeof (DebuggerDisplayAttribute), "set_TargetTypeName(System.String)")]