When calling the `bitmap(chunk)` method of the various *MarkingState accessors
we would receive a raw `Bitmap` pointer which does not tell you if accesses to
markbits should be made atomically or not. As a result, we would default to
doing atomic operation when in fact it may not be necessary.

Here we're introducing a templated `ConcurrentBitmap` class that wraps
operations done on the markbits and allows them to be made non-atomic.

Additionaly, some of the `Bitmap` methods were only used to verify the heap and
in the tests so they do not need atomic implementations. Using them in a
concurrent context should now fail to link to make sure they're not mis-used in
the future.

Change-Id: Ifb55f8522c8bf0c87d65da9227864ee428d21bbd
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Reviewed-on: https://chromium-review.googlesource.com/c/1482916Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#59836}