bento_button: Add focus support to the new desk bar

This change adds focus support to the new desk bar. The new bar will use
the default focus manager from the view tree, while the overview bar
will continue to use a customized overview highlight controller.

Please note that this change introduces the following differences in bar
behaviors:
  - When tabbing in the desk name view, the overview bar only highlights
    the view, but does not focus. The new bar will focus directly.
  - When committing a name change for the desk name view, the overview
    bar uses a cached highlighted view to re-claim focus to re-edit. The
    new bar does not support this.

Bug: b/277988182, b/287118621
Test: DeskBarTest.{DeskRenameKeyTab,DeskRenameKeyShiftTab,AutoHideKeyEsc,AutoHideKeyBack,ForwardTabbing,ReverseTabbing,CloseActiveDesk,MergeActiveDesk,CloseNonActiveDesk,MergeNonActiveDesk}
Change-Id: I6861e7db096cfc3183bd0f23bd60e985a1c97ee5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4633855
Commit-Queue: Yongshun Liu <yongshun@chromium.org>
Reviewed-by: Daniel Andersson <dandersson@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1168373}