implement skip_autocommit_rollback

implement skip_autocommit_rollback

Added new parameter :paramref:`.create_engine.skip_autocommit_rollback`
which provides for a per-dialect feature of preventing the DBAPI
``.rollback()`` from being called under any circumstances, if the
connection is detected as being in "autocommit" mode.   This improves upon
a critical performance issue identified in MySQL dialects where the network
overhead of the ``.rollback()`` call remains prohibitive even if autocommit
mode is set.

Fixes: #12784
Change-Id: I22b45ab2fc396c5aadeff5cdc5ce895144d00098