Revert "[regexp] Reorganize and deduplicate in the regexp parser"

This reverts commit 7d849870.

Reason for revert: Will block roll. Broke error message tests upstream:

https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Blink%20Win/6635/overview


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}

Change-Id: Ic7404d6c9f0e6ea51e8cd8f1ab672856dca0c637
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3190692
Auto-Submit: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#77125}

test/mjsunit/regress/regress-v8-10602.js

-// Copyright 2021 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-assertThrows(String.raw`/[\k](?<a>)/.exec()`);