add CTE cache elements for CompoundSelect, more verify tests

add CTE cache elements for CompoundSelect, more verify tests

Follow up of :ticket:`11471` to fix caching issue where using the
:meth:`.CompoundSelectState.add_cte` method of the
:class:`.CompoundSelectState` construct would not set a correct cache key
which distinguished between different CTE expressions. Also added tests
that would detect issues similar to the one fixed in :ticket:`11544`.

Fixes: #11471
Change-Id: Iae6a91077c987d83cd70ea826daff42855491330