Fix parameter mutation in orm_pre_session_exec()

Fix parameter mutation in orm_pre_session_exec()

The :meth:`_events.SessionEvents.do_orm_execute` event now allows direct
mutation or replacement of the :attr:`.ORMExecuteState.parameters`
dictionary or list, which will take effect when the the statement is
executed.  Previously, changes to this collection were not accommodated by
the event hook.  Pull request courtesy Shamil.

Fixes: #12921
Closes: #12989
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12989
Pull-request-sha: 86b64e06178f8722f1c1700fd9fcca53ca572e78

Change-Id: I04874b6ca720eb2be1470067ced4afd79896e267