Introduce a lock screen fadeout, adjust timings

Instead of just fading in the home wallpaper in front of the lock
wallpaper, introduce a crossfade.

The "wallpaperTargets", representing the wallpaper on home screen, has
been renamed to "openingWallpaperTargets". A similar
"closingWallpaperTargets" has been added for the lock screen wallpaper
that goes away.

Also make a similar transition when the keyguard is dismissed with a
swipe.

Restore some constants that were (wrongly!) changed under the flag.

Flag: com.android.systemui.faster_unlock_transition
Bug: 298186160
Test: manual, keyguard tests
Change-Id: I8e53fbb6f4d9949c712862dd5a3519d722a3dc8e