Add do_setinputsizes event for cx_Oracle

Add do_setinputsizes event for cx_Oracle

Added a new event currently used only by the cx_Oracle dialect,
:meth:`.DialectEvents.setiputsizes`.  The event passes a dictionary of
:class:`.BindParameter` objects to DBAPI-specific type objects that will be
passed, after conversion to parameter names, to the cx_Oracle
``cursor.setinputsizes()`` method.  This allows both visibility into the
setinputsizes process as well as the ability to alter the behavior of what
datatypes are passed to this method.

Change-Id: I43b97c8e3c840cad6f01edb274dc9cfed19cb5fc
Fixes: #4290