Improve resiliency when rooting broken assemblies (#103962)

Do a couple more upfront checks to trigger exceptions when it's recoverable. Fixes #103843.

We still eventually crash when generating debug information since we don't have fine grained tracking of what parts of the type we looked at. The user would need to drop debug info generation, or stop feeding us garbage.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/LibraryRootProvider.cs

@@ -99,9 +99,7 @@ public static void CheckCanGenerateMethod(MethodDesc method)
 
         private static void CheckTypeCanBeUsedInSignature(TypeDesc type)
         {
-            MetadataType defType = type as MetadataType;
-
-            defType?.ComputeTypeContainsGCPointers();
+            ((CompilerTypeSystemContext)type.Context).EnsureLoadableType(type);
         }
     }
 }

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/RootingServiceProvider.cs

@@ -46,7 +46,14 @@ public void AddCompilationRoot(TypeDesc type, string reason)
 
         public void AddReflectionRoot(TypeDesc type, string reason)
         {
-            _factory.TypeSystemContext.EnsureLoadableType(type);
+            TypeDesc lookedAtType = type;
+            do
+            {
+                _factory.TypeSystemContext.EnsureLoadableType(lookedAtType);
+                lookedAtType = (lookedAtType as MetadataType)?.ContainingType;
+            }
+            while (lookedAtType != null);
+
             _rootAdder(_factory.ReflectedType(type), reason);
         }
 
@@ -64,6 +71,7 @@ public void AddReflectionRoot(FieldDesc field, string reason)
             if (!_factory.MetadataManager.IsReflectionBlocked(field))
             {
                 _factory.TypeSystemContext.EnsureLoadableType(field.OwningType);
+                _factory.TypeSystemContext.EnsureLoadableType(field.FieldType);
                 _rootAdder(_factory.ReflectedField(field), reason);
             }
         }