[Launcher] Add MRFU cache logic.

This will be used by the various new rankers in a follow-up CL. See the
header comment in mrfu_cache.h for more details.

Bug: 1199206
Change-Id: Iddf65375b97e0e977a158383d233a62377d627f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3115519


Commit-Queue: Tony Yeoman <tby@chromium.org>
Reviewed-by: Amanda Deacon <amandadeacon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#915147}