Add hot reload test that adds custom attributes (#53387)

Add hot reload test that adds custom attributes (#53387)

* Add hot reload test that adds custom attributes

   This test adds new rows to the CustomAttribute table with both new a class and a new method as parents.  That should result in an unsorted table, which CoreCLR should be able to handle.

* rework the test not to rely on Assembly.GetType

   Looking up the new class using System.Reflection.Assembly.GetType wasn't working.

* clear reflection caches