Allow NUMERIC()/DECIMAL() IDENTITY columns

Allow NUMERIC()/DECIMAL() IDENTITY columns

Fixed issue where :class:`.Table` objects that made use of IDENTITY columns
with a :class:`.Numeric` datatype would produce errors when attempting to
reconcile the "autoincrement" column, preventing construction of the
:class:`.Column` from using the :paramref:`.Column.autoincrement` parameter
as well as emitting errors when attempting to invoke an :class:`.Insert`
construct.

Fixes: #8111
Change-Id: Iaacc4eebfbafb42fa18f9a1a4f43cb2b6b91d28a