Emit a better diagnostic when function actually has a 'self' parameter

Emit a better diagnostic when function actually has a 'self' parameter

Fixes #66898

When we are unable to resolve a reference to `self`, we current assume
that the containing function doesn't have a `self` parameter, and
emit an error message accordingly.

However, if the reference to `self` was created by a macro invocation,
then resolution will correctly fail, due to hygiene. In this case, we
don't want to tell the user that the containing fuction doesn't have a
'self' paramter if it actually has one.

This PR checks for the precense of a 'self' parameter, and adjusts the
error message we emit accordingly.

TODO: The exact error message we emit could probably be improved. Should
we explicitly mention hygiene?