This updates MicrotaskQueue to use pointer-compression style object
reference.

Bug: v8:8124
Change-Id: I7bef92a8760609f3045d2025b145b9a0ec880424
Reviewed-on: https://chromium-review.googlesource.com/c/1478320
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59762}