This adds support for tracing memory operations in code compiled with
Liftoff. This is the first runtime call we emit from Liftoff code, so
part of this code can be reused for other runtime calls.

Drive-by: Reuse outer compilation zone (avoid one Zone allocation).

Bug: v8:6600, v8:7210
Change-Id: I8b22088d0685338d533d328cb371384210e0ed22
Reviewed-on: https://chromium-review.googlesource.com/864663Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50652}