Add LocalHandleScope to allow for local handles in LocalHeaps
(background threads). This class is similar to HandleScope which still
needs to be used on the main thread. When performing a GC, the main
thread halts all background threads at a safepoint such that it can
safely iterate their roots.

Bug: v8:10315
Change-Id: Id8f5d54cc2535e004081ccdef15dc03a39b2d0f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2111218
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66853}