Merges `NativeModuleModificationScope` (with an implementation using
Intel PKU, if available, and mprotect otherwise) and
`CodeSpaceWriteScope` (for Apple Silicon, where switching to RWX with
mprotect is disallowed anyway, so MAP_JIT and thread-local switching
must be used).

Because `CodeSpaceWriteScope` sounded better (and is shorter), we kept
its name (which unfortunately makes the diff a bit harder to read).

R=clemensb@chromium.org
CC=jkummerow@chromium.org

Bug: v8:11714

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Change-Id: Ib2a7d18e72797a725ed34b904c70769166d811dd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972911Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Daniel Lehmann <dlehmann@google.com>
Cr-Commit-Position: refs/heads/master@{#75272}