Support for Create Table As

Support for Create Table As

Added support for the SQL ``CREATE TABLE ... AS SELECT`` construct via the
new :class:`_sql.CreateTableAs` DDL construct and the
:meth:`_sql.SelectBase.into` method. The new construct allows creating a
table directly from the results of a SELECT statement, with support for
options such as ``TEMPORARY`` and ``IF NOT EXISTS`` where supported by the
target database.  Pull request courtesy Greg Jarzab.

Fixes: #4950
Closes: #12860
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12860
Pull-request-sha: 7de8a109b892fd91222ce2f59c388ca275021ddb

Change-Id: Id9c8e4a3c520ffc61de1e48e331b6220e3d52fc9