ILLink : Test API expsure (#114567)

Re-expose `ReconstructedFullTypeName`.  We rely on this in our test framework

Expose `VerifyILOfOtherAssemblies`.  This causes us problems for our tests that verify the old mono BCL.  There's a goofy circular reference with Mono.Security.dll and System.dll which results in references to System.dll with two different PublicKeyTokens.  Exposing this method let's us disable this asserting behavior for our old mono tests

Author: mrvoorhe

src/tools/illink/test/Mono.Linker.Tests/TestCases/TestCase.cs

@@ -24,7 +24,7 @@ public TestCase (NPath sourceFile, NPath rootCasesDirectory, NPath originalTestC
 
 			// A little hacky, but good enough for name.  No reason why namespace & type names
 			// should not follow the directory structure
-			reconstructedFullTypeName = $"{sourceFile.Parent.RelativeTo (rootCasesDirectory.Parent).ToString (SlashMode.Forward).Replace ('/', '.')}.{sourceFile.FileNameWithoutExtension}";
+			ReconstructedFullTypeName = $"{sourceFile.Parent.RelativeTo (rootCasesDirectory.Parent).ToString (SlashMode.Forward).Replace ('/', '.')}.{sourceFile.FileNameWithoutExtension}";
 
 			var firstParentRelativeToRoot = SourceFile.RelativeTo (rootCasesDirectory).Elements.First ();
 			TestSuiteDirectory = rootCasesDirectory.Combine (firstParentRelativeToRoot);
@@ -40,7 +40,7 @@ public TestCase (NPath sourceFile, NPath rootCasesDirectory, NPath originalTestC
 
 		public NPath OriginalTestCaseAssemblyPath { get; }
 
-		private string reconstructedFullTypeName;
+		public string ReconstructedFullTypeName { get; }
 
 		public bool HasLinkXmlFile {
 			get { return SourceFile.ChangeExtension ("xml").FileExists (); }
@@ -59,7 +59,7 @@ public NPath LinkXmlFile {
 
 		public TypeDefinition FindTypeDefinition (AssemblyDefinition caseAssemblyDefinition)
 		{
-			var typeDefinition = caseAssemblyDefinition.MainModule.GetType (reconstructedFullTypeName);
+			var typeDefinition = caseAssemblyDefinition.MainModule.GetType (ReconstructedFullTypeName);
 
 			// For all of the Test Cases, the full type name we constructed from the directory structure will be correct and we can successfully find
 			// the type from GetType.

src/tools/illink/test/Mono.Linker.Tests/TestCasesRunner/ResultChecker.cs

@@ -135,7 +135,7 @@ bool HasActiveSkipKeptItemsValidationAttribute (ICustomAttributeProvider provide
 			}
 		}
 
-		void VerifyILOfOtherAssemblies (TrimmedTestCaseResult linkResult)
+		protected virtual void VerifyILOfOtherAssemblies (TrimmedTestCaseResult linkResult)
 		{
 			foreach (var linkedAssemblyPath in linkResult.Sandbox.OutputDirectory.Files ("*.dll")) {
 				if (linkedAssemblyPath == linkResult.OutputAssemblyPath)