Merge "Let Talkback announce to the user when changing dark/light theme" into sc-v2-dev am: 13673f84a6 am: 933fda3ea5

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/16373914

Change-Id: Ic20614adaa8b405cefb4eb9b47080c4eda5d1db7