No functional changes.

- Removed unused Isolate* argument from regexp extrefs.
- Added const where possible.
- Removed unused functions.
- Shuffled declarations for better readability.
- ...

Change-Id: I6d9093052e8de4e33e9411541a691d0bab7b20c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3217193
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77316}