Reland: Implements the aod appearing transition

This is to show lock wallpaper according to transition
lifecycle. WmCore requests the appearing transition when
aod is showing. And then, transition collects all wallpapers
including system and lock. KeyguardService can apply
cross-fade animation for wallpapers.

Also, separate the aod appearing and keyguard appearing transition.

When aod is changed without keyguard changed, keyguard appearing
flag is set unnecessarily. This may confuse keyguard service.

Also, when aod changes while feature is turned off, keyguard appearing
transition may operate causing problems.

We only enable code to send keygaurd appearing. if keyguardChanged and
only enable code to send aod if aodChanged. This is more in line with
what the original code was doing and wouldn't introduce any new behavior
with the flag turned off.

It is related to commit 649a78d2

Bug: 361438779
Test: Manual: feature off; turn screen off to go aod state
Test: Manual: Setup lock wallpaper; Turn screen off to go aod state
Flag: com.android.window.flags.aod_transition
Change-Id: I6f0067de2a754c25515a6cc4bc8c9dcfb78ede80