Fix Type.GetHashCode for RuntimeTypes w/o MethodTable (dotnet#97195)

The hashcode for these was always 0 before this change.

src/coreclr/nativeaot/System.Private.CoreLib/src/System/RuntimeType.cs

@@ -204,7 +204,12 @@ public override Array GetEnumValuesAsUnderlyingType()
         }
 
         public override int GetHashCode()
-            => ((nuint)_pUnderlyingEEType).GetHashCode();
+        {
+            MethodTable* pEEType = _pUnderlyingEEType;
+            if (pEEType != null)
+                return ((nuint)pEEType).GetHashCode();
+            return RuntimeHelpers.GetHashCode(this);
+        }
 
         public override RuntimeTypeHandle TypeHandle
         {