Float and Numeric aren't set as autoincrement

Float and Numeric aren't set as autoincrement

The :class:`.Float` and :class:`.Numeric` types are no longer automatically
considered as auto-incrementing columns when the
:paramref:`_schema.Column.autoincrement` parameter is left at its default
of ``"auto"`` on a :class:`_schema.Column` that is part of the primary key.
When the parameter is set to ``True``, a :class:`.Numeric` type will be
accepted as an auto-incrementing datatype for primary key columns, but only
if its scale is explicitly given as zero; otherwise, an error is raised.
This is a change from 2.0 where all numeric types including floats were
automatically considered as "autoincrement" for primary key columns.

Fixes: #11811
Change-Id: Icdfe084d425166199d6647335c5b53ea5b4b416e