Ensure that page header flags are properly initialized before concurrent markers can discover objects.

Bug: v8:10315
Change-Id: Ib9ce813dfd3fda75e4ee209a846828366222b110
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2198990Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67775}