Nullability: RuntimeHelpers.GetHashCode should accept null obj input (#31819)

Author: GrabYourPitchforks

src/coreclr/src/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.CoreCLR.cs

@@ -107,7 +107,7 @@ public static void PrepareMethod(RuntimeMethodHandle method, RuntimeTypeHandle[]
         public static extern void PrepareDelegate(Delegate d);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
-        public static extern int GetHashCode(object o);
+        public static extern int GetHashCode(object? o);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         public static extern new bool Equals(object? o1, object? o2);

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -7273,7 +7273,7 @@ public static partial class RuntimeHelpers
         public static void EnsureSufficientExecutionStack() { }
         public static new bool Equals(object? o1, object? o2) { throw null; }
         public static void ExecuteCodeWithGuaranteedCleanup(System.Runtime.CompilerServices.RuntimeHelpers.TryCode code, System.Runtime.CompilerServices.RuntimeHelpers.CleanupCode backoutCode, object? userData) { }
-        public static int GetHashCode(object o) { throw null; }
+        public static int GetHashCode(object? o) { throw null; }
         [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNullAttribute("obj")]
         public static object? GetObjectValue(object? obj) { throw null; }
         public static T[] GetSubArray<T>(T[] array, System.Range range) { throw null; }

src/mono/netcore/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.Mono.cs

@@ -20,9 +20,9 @@ public static int OffsetToStringData {
 		}
 
 		[MethodImplAttribute (MethodImplOptions.InternalCall)]
-		static extern int InternalGetHashCode (object o);
+		static extern int InternalGetHashCode (object? o);
 
-		public static int GetHashCode (object o)
+		public static int GetHashCode (object? o)
 		{
 			return InternalGetHashCode (o);
 		}