annotated / DC forms for association proxy

annotated / DC forms for association proxy

Added support for the :func:`.association_proxy` extension function to
take part within Python ``dataclasses`` configuration, when using
the native dataclasses feature described at
:ref:`orm_declarative_native_dataclasses`.  Included are attribute-level
arguments including :paramref:`.association_proxy.init` and
:paramref:`.association_proxy.default_factory`.

Documentation for association proxy has also been updated to use
"Annotated Declarative Table" forms within examples, including type
annotations used for :class:`.AssocationProxy` itself.

Also modernized documentation examples in sqlalchemy.ext.mutable,
which was not up to date even for 1.4 style code.

Corrected typing for relationship(secondary) where "secondary"
accepts a callable (i.e. lambda) as well

Fixes: #8878
Fixes: #8876
Fixes: #8880
Change-Id: Ibd4f3591155a89f915713393e103e61cc072ed57