When a compaction space allocates a new code page, that pages needs to
be added to the Isolate::code_pages_ array used for stack unwinding.
Since the array is owned by the main thread, compaction thread cannot
directly modify it. Because of that code pages are added upon merging
of the compaction space to the main spage in MergeLocalSpace.

The bug was that all code pages coming from the compaction space
were added to the code_pages_ array. However, some of the pages are
not newly allocated but merely borrowed from the main space.

This CL introduces a new page flag for marking pages that are borrowed
during compaction and skips them in MergeLocalSpace.

Bug: v8:10900
Change-Id: I786dc5747bd7c785ae58dfd8b841c00774efb15e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2416500Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69992}