Move expansion of the new space into the safepoint. Otherwise background
threads race with the main thread when accessing the new space capacity.
This will most likely also be required to allow the allocation of new
space objects from background threads.

Reland of https://crrev.com/c/2235539, the timeouts were unrelated to this CL.

Bug: v8:10315
Change-Id: I134b4f27ec666cf036c346b847d164255e0fe7d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2237626Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68284}