Factor Read Anything font utils to new file and improve.

Instead of directly traversing global data at multiple call sites,
encapsulate behind a simple pair of functions. Then cache the results
when the base language changes instead of recomputing on each request.

This leads to simpler and faster callsites and less data in headers.

Also simplify test code using ElementsAre() while I'm at it.

NO_IFTTT=Bogus warning

Bug: 364987728
Change-Id: I8a7602867b793138541d623d1aa85bb726657c06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6278591
Reviewed-by: Abigail Klein <abigailbklein@google.com>
Reviewed-by: Mark Schillaci <mschillaci@google.com>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Abigail Klein <abigailbklein@google.com>
Cr-Commit-Position: refs/heads/main@{#1422062}