rename MappedCollection and related

rename MappedCollection and related

For consistency with the prominent ORM concept :class:`_orm.Mapped`, the
names of the dictionary-oriented collections,
:func:`_orm.attribute_mapped_collection`,
:func:`_orm.column_mapped_collection`, and :class:`_orm.MappedCollection`,
are changed to :func:`_orm.attribute_keyed_dict`,
:func:`_orm.column_keyed_dict` and :class:`_orm.KeyFuncDict`, using the
phrase "dict" to minimize any confusion against the term "mapped". The old
names will remain indefinitely with no schedule for removal.

Docs here are also updated for typing as we can type
these collections as ``Mapped[dict[str, cls]]``, don't need
KeyFuncDict / MappedCollection for these

Fixes: #8608
Change-Id: Ib5cf63e0aef1c389e023a75e454bb21f9d779b54