this will allow to add raw fields to the native context in a pointer compression
friendly way.

This CL also adds a microtask_queue field to native context which will be used
in a follow-up CL.

Bug: v8:8238, v8:7703
Change-Id: I5ecf72dbc52e8261b694551cbc8476f967967723
Reviewed-on: https://chromium-review.googlesource.com/c/1348073
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57744}