We currently trigger a GC when creating a module while the remaining
uncommitted code space is below 32MB. For bigger modules, this is not
enough. Instead, make this limit relative: Trigger GC if we fall below
50% of the available code space, and re-adjust this limit after each GC
to avoid repeated GCs that do not free anything.

R=ahaas@chromium.org

Bug: v8:8624
Change-Id: I7abfad3b57663d528a26d29232ad6bc2dc63cef4
Reviewed-on: https://chromium-review.googlesource.com/c/1391753Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58527}