Add generic attribute instance dataflow tests

[M]aybe create an issue to add tests which do some simple validation of data flow stuff on the generic instantiations of attributes.
I'm not worried about linker, but analyzer and AoT might have problems.

_Originally posted by @vitek-karas in https://github.com/dotnet/linker/pull/2980#pullrequestreview-1082623317_

https://github.com/dotnet/linker/pull/2980#pullrequestreview-1082623317 adds support for generic attributes, but we could use more testing that validates basic dataflow, as per the suggestion.