Generic TestCase and TestCaseParameter support

[stevenaw]

As a follow-up to #1215
Where we allowed the passing of Type objects in a TypeArgs property to allow consumers greater control over the type arguments used in generic test methods.

This would allow the creation of generically-typed TestCase attribute. We may want to provide a few overloads here to account for up to n different strongly typed args.

This would be on modern (NET 6+) frameworks. See a sample snippet here: #4620 (comment)