[mono] Support AcceptByRefLike metadata generic param attribute

Contributes to #94415 (and ultimately to #65112)

The metadata design is specced out here: https://github.com/dotnet/runtime/blob/main/docs/design/features/byreflike-generics.md

There are tests in https://github.com/dotnet/runtime/tree/main/src/tests/Loader/classloader/generics/ByRefLike