RwxMemoryWriteScope becomes the bottleneck for both MAP_JIT and PKU
machinery.
Wasm and V8 code space will use the same memory protection key.

This is a next step towards adding PKU support for V8 code space.

Bug: v8:13023
Change-Id: I647f8c09bc41e5ef8a1d74b58a48a43e08454e0d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3702213Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Wenqin Yang <wenqin.yang@intel.com>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81947}