Supporting both RequiresUnreferencedCode and DynamicallyAccessedMembers annotations on a method

[eerhardt]

In dotnet/runtime#47938, we are annotating a method with both RequiresUnreferencedCode and DynamicallyAccessedMembers attributes. This should do both:

• Raise an ILLink warning when someone calls it
• Preserve the necessary members that are dynamically accessed.

See dotnet/runtime#47938 (comment).

The scenario here is that part of a method may be trim compatible (like using Reflection to find a method by name), but another part may be incompatible (like calling MakeGenericMethod if the caller passed in a Type[] typeArguments value).

We should ensure this scenario works as expected.

[vitek-karas]

The intended behavior is:

• Callers will get a warning due to the RequiresUnreferencedCode
• Callers will apply the requirements of the DynamicallyAccessedMembers on the method parameters
• The method body will not produce data flow warnings
• The method body is still fully analyzed and if it adds requirements on something that will be applied

#1827 adds a test to validate this - but it already works that way.

[vitek-karas]

As noted above, the behavior is already as expected and the test coverage has been merged.