Issue #21205: Add a new ``__qualname__`` attribute to generator, the qualified

Issue #21205: Add a new ``__qualname__`` attribute to generator, the qualified
name, and use it in the representation of a generator (``repr(gen)``). The
default name of the generator (``__name__`` attribute) is now get from the
function instead of the code. Use ``gen.gi_code.co_name`` to get the name of
the code.