Stack transfers consist of a number of register moves plus a number of
register loads. We currently store both in separate vectors. This CL
changes that to be stored in arrays indexed by the destination register
(such that it behaves like a map). This avoids any dynamically growing
structures.

Measured locally, this speeds up stack transfer processing by ~10%,
which translates to ~0.5% of overall Liftoff compilation time.

R=ahaas@chromium.org

Bug: v8:6600, v8:8423
Change-Id: Id532960dcc12f228507ed75e392ad4c57710593f
Reviewed-on: https://chromium-review.googlesource.com/c/1396278
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58587}