Fix typing to ensure that InstrumentedAttribute is hashable

Fix typing to ensure that InstrumentedAttribute is hashable

Repaired the core "SQL element" class ``SQLCoreOperations`` to support the
``__hash__()`` method from a typing perspective, as objects like
:class:`.Column` and ORM :class:`.InstrumentedAttribute` are hashable and
are used as dictionary keys in the public API for the :class:`_dml.Update`
and :class:`_dml.Insert` constructs.  Previously, type checkers were not
aware the root SQL element was hashable.

Fixes: #10353
Change-Id: I3c8eeb7ceb29a3087596e17d09aa6a7f45a8cf99