This CL creates trampolines into binary-embedded builtins on
isolate-creation, if --stress-off-heap-code is passed.

Note that this still overwrites existing code objects with the
off-heap trampoline, and that off-heap builtins still exist both in
the snapshot and the binary. Addressing these points are the next
steps.

Drive-by-change: More efficient off-heap code lookups now that the
off-heap memory area has a contiguous and static layout.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:6666
Change-Id: I7e7ef0aa2cd7b8184ae3a13fa02bdcbb4f2c9f86
Reviewed-on: https://chromium-review.googlesource.com/947969
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51809}