swift234

SILGen: Always open-code materializeForSet

This improves MaterializeForSetEmitter to support emission
of static materializeForSet thunks, as well as witnesses.

This is now done by passing in a nullptr as the conformance
and requirement parameters, and adding some conditional code.

Along the way, I fixed a few limitations of the old code,
namely weak/unowned and static stored properties weren't
completely plumbed through. There was also a memory leak in
addressed materializeForSet, the valueBuffer was never freed.

Finally, remove the materializeForSet synthesis in Sema since
it is no longer needed, which fixes at least one known crash
case.