Fix RunClassConstructor trim warning for Nullable<T> (#106975)

The trimming tools (ILLink, native AOT, and the trim analyzer) report
warnings when RunClassConstructor is called for nullable value
types. This is not problematic for trimming and should not warn.

Author: sbomer

src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCases/TestSuites.cs

@@ -74,6 +74,7 @@ public void Reflection (string t)
 			case "ParametersUsedViaReflection":
 			case "UnsafeAccessor":
 			case "TypeUsedViaReflection":
+			case "RunClassConstructor":
 				Run (t);
 				break;
 			default:

src/tools/illink/src/ILLink.Shared/TrimAnalysis/HandleCallAction.cs

@@ -293,6 +293,8 @@ ValueWithDynamicallyAccessedMembers valueWithDynamicallyAccessedMembers
 					} else if (typeHandleValue is RuntimeTypeHandleForValueWithDynamicallyAccessedMembers damAnnotatedHandle
 						&& (damAnnotatedHandle.UnderlyingTypeValue.DynamicallyAccessedMemberTypes & DynamicallyAccessedMemberTypes.NonPublicConstructors) != 0) {
 						// No action needed, NonPublicConstructors keeps the static constructor on the type
+					} else if (typeHandleValue is RuntimeTypeHandleForNullableSystemTypeValue) {
+						// No action needed, RunClassConstructor does not run the class constructor of the underlying type of Nullable<T>
 					} else {
 						_diagnosticContext.AddDiagnostic (DiagnosticId.UnrecognizedTypeInRuntimeHelpersRunClassConstructor, calledMethod.GetDisplayName ());
 					}

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/ReflectionTests.cs

@@ -166,6 +166,12 @@ public Task PropertiesUsedViaReflection ()
 			return RunTest ();
 		}
 
+		[Fact]
+		public Task RunClassConstructor ()
+		{
+			return RunTest ();
+		}
+
 		[Fact]
 		public Task RuntimeReflectionExtensionsCalls ()
 		{

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

@@ -49,12 +49,6 @@ public Task ParametersUsedViaReflection ()
 			return RunTest (allowMissingWarnings: true);
 		}
 
-		[Fact]
-		public Task RunClassConstructorUsedViaReflection ()
-		{
-			return RunTest (allowMissingWarnings: true);
-		}
-
 		[Fact]
 		public Task UnderlyingSystemType ()
 		{

src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/RunClassConstructorUsedViaReflection.cs renamed to src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/RunClassConstructor.cs

@@ -8,7 +8,7 @@ namespace Mono.Linker.Tests.Cases.Reflection
 {
 	[SetupCSharpCompilerToUse ("csc")]
 	[ExpectedNoWarnings]
-	public class RunClassConstructorUsedViaReflection
+	public class RunClassConstructor
 	{
 		public static void Main ()
 		{
@@ -21,6 +21,7 @@ public static void Main ()
 			TestPublicConstructorDataFlowType ();
 			TestIfElseUsingRuntimeTypeHandle (1);
 			TestIfElseUsingType (1);
+			TestNullableValueType ();
 		}
 
 		[Kept]
@@ -125,6 +126,12 @@ static void TestIfElseUsingType (int i)
 			RuntimeHelpers.RunClassConstructor (myType.TypeHandle);
 		}
 
+		[Kept]
+		static void TestNullableValueType ()
+		{
+			RuntimeHelpers.RunClassConstructor (typeof (int?).TypeHandle);
+		}
+
 		[Kept]
 		[KeptMember (".cctor()")]
 		class OnlyUsedViaReflection