- move cte tests into their own test/sql/test_cte.py

- move cte tests into their own test/sql/test_cte.py
- rework bindtemplate system of "numbered" params by applying
the numbers last, as we now need to generate these out of order
in some cases
- add positional assertion to assert_compile
- add new cte_positional collection to track bindparams generated
within cte visits; splice this onto the beginning of self.positiontup
at cte render time, [ticket:2521]