make local mutable copies for cargs / cparams in do_connect

make local mutable copies for cargs / cparams in do_connect

Fixed a critical issue in :class:`.Engine` where connections created in
conjunction with the :meth:`.ConnectionEvents.do_connect` event listeners
would receive shared, mutable collections for the connection arguments,
leading to a variety of potential issues including unlimited growth of the
argument list as well as elements within the parameter dictionary being
shared among concurrent connection calls.  In particular this could impact
do_connect routines making use of complex mutable authentication
structures.

Fixes: #13144
Change-Id: I1549dae36e8e7e6cf50fdaf796659b53e7b78234