Add PhraseTiming interface for Read Aloud text highlighting

Bug: b/296280100
Change-Id: If258417640edc2ca3bc94aa4a49a7b42f9f2d749
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4785414


Reviewed-by: Basia Zimirska <basiaz@google.com>
Auto-Submit: Ian Wells <iwells@chromium.org>
Commit-Queue: Basia Zimirska <basiaz@google.com>
Cr-Commit-Position: refs/heads/main@{#1184819}