This fast path works for ASCII-only strings and is similar to the
existing fast-path in C++. Important differences:
- The locale check is done at Turbofan optimization time instead of
  at runtime
- Use tables of size 256 instead of 128 to save a bounds-check when
  handling one-byte strings.
- It first performs an equality check that's optimized for detecting
  inequality quickly by comparing the strings from both ends. If the
  equality check succeeds, we are done. Otherwise chances are high
  that the strings differ according to collation level L1 already.
  Therefore, we first do an L1 check and perform the L3 check
  only when L1 didn't find a difference. This is based on the assumption
  that few strings are identical except for different capitalization.
- Use the Torque version of string flattening instead of the runtime
  version.

Bug: v8:12196
Change-Id: I2d043c1138846783f6d567b736d34063ba9301e5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3268465Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77946}