Compile the 'on' clause of a merge into statement

[TRManderson]

I had a use case where my on clause made use of sqlalchemy.func and thus had a bind param in it, and without getting the compiler to process the on clause before compiling it, it would have a dangling bind param that was never filled.

This fixes my use case. I was not able to run tests because I got a tox error on my mac, so I'm leaving it up to CI (sorry), but all my other Snowflake SQLA code works great with this fix.

[TRManderson]

Attempting converting to draft and back to trigger reviews

[TRManderson]

I'm extremely sure that the check failing here is due to misconfiguration, not my code, but there are no new changes on master that I can merge in to trigger a new test run