[ChromeVox] Update location when activeDescendant removed

ChromeVox previously ignored activeDescendant events when there was not
a current activeDescendant set. Update to re-focus the focus ring on
the target element, if it is the current focus.

AX-Relnotes: fix bug with focus ring location in lists.
Fixed: b/346465942, b/356222515
Change-Id: Idfecbf70832de38328c789768be8a2f3043b3956
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5750066
Auto-Submit: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1335113}