So far the main thread can have two different kinds of local handles,
regular main thread handles and local handles in its LocalIsolate. This
is both confusing and error-prone.

This CL retargets local handles creation for the LocalIsolate on the
main thread to always create regular main thread handles instead.

Bug: v8:10315
Change-Id: I4df509a0fc1bd630ba956b5eaacacbe706ddb4ef
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2527062Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71534}