Suspend points (inside generators and async functions) have slightly
funky semantics when it comes to liveness, as they save and restore a
chunk of the register file as-is. In particular, this means that
granular liveness information is lost, as it is assumed that all
registers in that chunk of the register file are live in a suspend.

Rather than marking that entire chunk of register as live/dead in
suspend/restore, we can instead pattern-match the set of bytecodes in a
suspend point, and propagate liveness across them. This tightens
liveness estimates, and could be used to optimize which values TurboFan
actually saves when suspending.

Bug: chromium:798137
Change-Id: I5840cdbfc2c6edb1d3a48cf025f52615b629cdfc
Reviewed-on: https://chromium-review.googlesource.com/848895
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50757}