Add flag to show lock wallpaper in aod state

This is a flag to show the lock wallpaper in aod state.
Currently, there is no policy for showing wallpaper for
appearing aod.

So it will be implemented so that the lock wallpaper can
be displayed when aod appears like keyguard appearing.

Bug: 361438779
Test: N/A - just a flag
Flag: com.android.window.flags.aod_transition
(cherry picked from https://partner-android-review.googlesource.com/q/commit:3ae2b96dfc5a74b92855299d51c4fcf4a18b5bb7)
Merged-In: Ibcb0b4ab5db4278380e474d1f40996de24244ff6
Change-Id: Ibcb0b4ab5db4278380e474d1f40996de24244ff6