Support SetM in new minstrs

Support SetM in new minstrs

Summary: This adds new final operation minstrs to handle SetM.

A few things worth calling out:
- The unwinder now DecRefs tvRef/tvRef2 if a minstr throws. This takes the
  place of the custom catch traces used by the old minstr instructions.
- FrameState supports member set operations that modify local/stack bases
  through pointers that don't come directly from LdLocAddr/LdStkAddr. This
  almost never happens in practice but now that we can break tracelets in the
  middle of a member operation, it's necessary for correctness. The current
  support is extremely conservative; if that turns out to be a problem it can
  be refined later.
- Added gen-time load-elim for the member base register, to preserve some of
  the optimizations done in irgen-minstr. Track the type when we have to give
  up on the specific value. We can stop relying on this if and when we move a
  lot of the logic in irgen-minstr to its own pass.
- Fixed a bug in relaxToGuardable() that was causing us to guard on StaticArr
  in a pseudomain. Also added an assert in codegen that will catch this if it
  happens again, rather than just emitting an incorrect guard.
- Fixed a couple places in member-operations.h where we were returning &tvRef
  with tvRef set to Uninit, violating the invariant that the result is &tvRef
  iff tvRef isn't Uninit.

Reviewed By: alexmalyshev

Differential Revision: D2507681

fb-gh-sync-id: 25ee0c2e3e9d0711f64457afe9eb435ca896899e