allow `module.__interface__` to be used in call position by adding it to
the module membership data structure.

additionally, fix a bug where interfaces defined inline could not be
exported. this is simultaneously fixed as a related bug because
previously, interfaces could come up in export analysis as `InterfaceT`
or `TYPE_T` depending on their provenance. this commit fixes the bug by
making them `TYPE_T` in both imported and inlined provenance.

refactor:
- wrap interfaces in TYPE_T
- streamline an `isinstance(t, (VyperType, TYPE_T))` check.
  `TYPE_T` now inherits from `VyperType`, so it doesn't need to be
  listed separately

there was a test for unimplemented `.vyi` interfaces, this commit adds a
test for unimplemented inline interface for completeness