Port 3e3a027d

Original Commit Message:

    Irregexp reentrancy (crrev.com/c/3162604) introduced a bug for global
    regexp execution in which each iteration would use a new stack region
    (i.e. we forgot to pop the regexp stack pointer when starting a new
    iteration).

    This CL fixes that by popping the stack pointer on the loop backedge.

    At a high level:

    - Initialize the backtrack_stackpointer earlier and avoid clobbering
      it by setup code.
    - Pop it on the loop backedge.
    - Slightly refactor Push/Pop operations to avoid unneeded memory
      accesses.

R=jgruber@chromium.org, joransiu@ca.ibm.com, junyan@redhat.com, midawson@redhat.com
BUG=
LOG=N

Change-Id: Iafe6814d3695e83fced6a46209accf5e712d56f6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3198391Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#77180}