Deprecate all functions for Unicode case insensitive matching

- Replace some "IgnoreCase" calls with "IgnoreASCIICase" versions if
  their behavior won't be changed.

This CL has no behavior changes.

Bug: 40476285
Change-Id: Idfce4feda1c8f6cd5898874a65e723e94ef4806d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6040043
Reviewed-by: Koji Ishii <kojii@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1386712}