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.
In order to fix some other issues that came up with materializeForSet
and resilience, I had to bite the bullet and finish off John's code
for open-coding materializeForSet emission in SILGen. This patch
makes the subsequent changes easier to review.
