This is a reland of 7d849870

Original change's description:
> [regexp] Reorganize and deduplicate in the regexp parser
>
> The parser is organized in a somewhat tricky way s.t. it can be
> hard to map the implementation back to the specified grammar.
>
> In particular, the logic for CharacterClassEscape, ClassEscape,
> and CharacterEscape was implemented twice - once inside a character
> class, once outside.
>
> This CL refactors related logic to have only a single implementation.
>
> As a drive-by, fix one related inconsistency related to \k inside
> a character class.
>
> Fixed: v8:10602
> Change-Id: I5858840159694fa6f8d1aa857027db80754e3dfd
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3178966
> Reviewed-by: Mathias Bynens <mathias@chromium.org>
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#77114}

Fixed: v8:10602,chromium:1253976
Change-Id: I9e7cc6a34d3be06e1a68895775aa50b0eee78c57
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3193531Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77135}