[xaprepare] Generate omnisharp.json for the current branch (#7166)

Context: https://github.com/OmniSharp/omnisharp-roslyn/wiki/Configuration-Options

Update `xaprepare` to generate an `omnisharp.json` file in the top-
level directory.  The generated `omnisharp.json` should allow any
editor using [OmniSharp][0] to open samples, solutions, projects, and
tests in the xamarin-android tree which use .NET 7, allowing such
projects to have full code completion/etc.

Note that `omnisharp.json` will affect only the xamarin-android
checkout.  If you want to be able to open projects outside the
xamarin-android source tree, the generated file needs to be copied
(or symlinked) into `$HOME/.omnisharp/` or to the root of the project
being opened.

[0]: https://www.omnisharp.net/

Author: grendello

.gitignore

@@ -28,3 +28,4 @@ tests/api-compatibility/reference/*.cs
 Novell
 *.patch
 *.keystore
+/omnisharp.json

build-tools/scripts/omnisharp.json.in

@@ -0,0 +1,17 @@
+{
+    "msbuild": {
+        "loadProjectsOnDemand": true,
+        "Configuration": "@CONFIGURATION@"
+    },
+
+    "RenameOptions": {
+        "RenameInComments": false,
+        "RenameOverloads": true,
+        "RenameInStrings": false
+    },
+
+    "sdk": {
+        "IncludePreleases": true,
+        "Path": "@DOTNET_SDK_PATH@"
+    }
+}

build-tools/xaprepare/xaprepare/Steps/Step_GenerateFiles.cs

@@ -62,6 +62,7 @@ protected override async Task<bool> Execute (Context context)
 						Get_mingw_32_cmake (context),
 						Get_mingw_64_cmake (context),
 						Get_MonoGitHash_props (context),
+						Get_Omnisharp_Json (context),
 					};
 				}
 			}
@@ -237,5 +238,21 @@ public GeneratedFile Get_MonoGitHash_props (Context context)
 				Path.Combine (Configurables.Paths.BuildBinDir, OutputFileName)
 			);
 		}
+
+		public GeneratedFile Get_Omnisharp_Json (Context context)
+		{
+			const string OutputFileName = "omnisharp.json";
+
+			var replacements = new Dictionary<string, string> (StringComparer.Ordinal) {
+				{ "@CONFIGURATION@", context.Configuration },
+				{ "@DOTNET_SDK_PATH@", Path.Combine (Configurables.Paths.DotNetPreviewPath, "sdk", context.Properties.GetRequiredValue (KnownProperties.MicrosoftDotnetSdkInternalPackageVersion)) },
+			};
+
+			return new GeneratedPlaceholdersFile (
+				replacements,
+				Path.Combine (Configurables.Paths.BuildToolsScriptsDir, $"{OutputFileName}.in"),
+				Path.Combine (BuildPaths.XamarinAndroidSourceRoot, OutputFileName)
+			);
+		}
 	}
 }