The following adds support for JSMember through the existing
GlobalHandles implementation also used for TracedReference.

In addition, JSMember now supports set, clear, copy, move, comparison
and interaction with Local.

Bug: chromium:1056170
Change-Id: Ia50218bcfe4c056b3533a5b14eea954ade1da243
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2310357Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69028}