Simplify logic to focus out of date cell view

Removes logic that was explicitly focusing next month and event list
view when focusing out of a date cell view.
Instead, rely on scroll view's focus order  defined in the calendar
view: temporarily focus the scroll view, and advance focus in the
desired direction, matching the current logic in case event list
is hidden, and shift key is not pressed.

This allows reverse tabbing out of calendar view if there are
glanceable bubble showing (focusing next month view ended up trapping
focus withing the calendar view, as the date cell view is the first
focused view in the calendar).

BUG=b:297186532

Change-Id: I55cb785a4db57cf1066820981971c6fbffb2ebcf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4812178
Reviewed-by: Jiaming Cheng <jiamingc@chromium.org>
Commit-Queue: Toni Barzic <tbarzic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1188568}