support NewType in type_annotation_map

support NewType in type_annotation_map

Added support for :pep:`484` ``NewType`` to be used in the
:paramref:`_orm.registry.type_annotation_map` as well as within
:class:`.Mapped` constructs. These types will behave in the same way as
custom subclasses of types right now; they must appear explicitly within
the :paramref:`_orm.registry.type_annotation_map` to be mapped.

Within this change, the lookup between decl_api._resolve_type
and TypeEngine._resolve_for_python_type is streamlined to not
inspect the given type multiple times, instead passing
in from decl_api to TypeEngine the already "flattened" version
of a Generic or NewType type.

Fixes: #9175
Change-Id: I227cf84b4b88e4567fa2d1d7da0c05b54e00c562