[Read Aloud] Add strings for the new highlight granularity menu

Bug: 356462367
Change-Id: I9141524b243d72c65dce014eb4aee2eac8c03bb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5805187


Auto-Submit: Kristi Saney <kristislee@google.com>
Reviewed-by: Lauren Winston <lwinston@google.com>
Commit-Queue: Kristi Saney <kristislee@google.com>
Cr-Commit-Position: refs/heads/main@{#1345151}