Merge pull request #2880 from kumpera/fix_5644

[verifier] Do method visibility checks for virtual final methods. Enable type visibility for all methods. Fixes #5644.

I cannot repro the issue mentioned in the comments of mono_method_can_access_method.

* FIXME:
* with generics calls to explicit interface implementations can be expressed
* directly: the method is private, but we must allow it. This may be opening
* a hole or the generics code should handle this differently.
* Maybe just ensure the interface type is public.

@monojenkins merge