Fix accessibility issues in history embeddings

- Add outline around focused results in high contrast mode
- Update screen reader messages to specify that exact match results
were found, to differentiate it from embeddings results.

(cherry picked from commit b0f0d2b1)

Fixed: 376520571, 376522142
Change-Id: Id228d548bc464db6d86642718ba55a0f16a1f97f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5980295


Reviewed-by: manuk hovanesian <manukh@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Original-Commit-Position: refs/heads/main@{#1376012}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5989031


Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Orin Jaworski <orinj@chromium.org>
Commit-Queue: Orin Jaworski <orinj@chromium.org>
Cr-Commit-Position: refs/branch-heads/6778@{#1666}
Cr-Branched-From: b21671ca-refs/heads/main@{#1368529}