Fix gir gst regression

[bruchar1]

No description provided.

[xclaesse]

@bruchar1 while I agree this fix this case, that means we need to do that in every single place we do isinstance(lib, build.SharedLibrary) in the whole Meson codebase. This is why I originally made BothLibraries subclass SharedLibrary. That got changed against my recommendation.

[xclaesse]

I think BothLibraries should exclusively be an interpreter concept. It's already a big mistake to even have that class in build.py, it should be an InterpreterObject inside interpreterobjects.py.

In build.py we need 2 classes (naming TBD):

class SharedLibraryWithStatic(SharedLibrary):
  def as_static(self):
    return self.static
class StaticLibraryWithShared(StaticLibrary):
  def as_shared(self):
    return self.shared

That way we are sure they are treaded exactly as a shared/static library everywhere, but we still can take their bother library for the specific case of as_shared() and as_static() methods.

[xclaesse]

@bruchar1 I made an alternative implementation in #13835. What do you think?

[bruchar1]

@bruchar1 I made an alternative implementation in #13835. What do you think?

I like the idea. I'm trying to fix it here, since I cannot write to your branch...