[regexp] Remove Zone usage in runtime-regexp.cc

.. to reduce memory overhead. Zones allocate a minimum segment size of
8KB, and the uses in runtime-regexp.cc are expected to need << that.

Two uses were replaced by SmallVectors:

* CompiledReplacement, parses string replacement patterns for
  optimized repeated use.
* Intermediate data structures in RegExpReplace.

Bug: v8:11540
Change-Id: I3fb2d047f1bfadc9b85132f731b294bd8aa72368
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2752873
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73349}