_handle_dbapi_exception_noconnection() to only invoke in the case
of raw_connection() in the constructor of Connection.   in all other
cases the Connection proceeds with _handle_dbapi_exception() including
revalidate.

to it, so that we say we will do the wrapping just once right here
in _execute_context() / _execute_default().  An adjustment is made
to _handle_dbapi_error() to not assume self.__connection in case
we are already in an invalidated state

further adjustment to
0639c199a547343d62134d2f233225fd2862ec45, 41e7253dee168b8c26c49, #3266

take effect in all engine connection use cases, including
when user-custom connect routines are used via the
:paramref:`.create_engine.creator` parameter, as well as when
the :class:`.Connection` encounters a connection error on
revalidation.
fixes #3266

to get all flake8 passing

- remove deprecated 0.7 engine methods