This CL adds the BUILTIN kind specific flag is_off_heap_trampoline
to Code objects. Code objects hence know whether they are off-heap
trampolines, and can decide whether they need to return the off-heap
instruction start or not without looking at the builtin index and/or
considering the existence of an embedded blob.

Bug: v8:6666
Change-Id: I0fbc540a2624ed5fa8256b807299e2fe4b907dda
Reviewed-on: https://chromium-review.googlesource.com/1109691
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53956}