Enable AOD image wallpaper and apply aod mask view.

1. Enables image wallpaper in AOD.
2. Enables a mask with 70% black scrim and vignette effects.
3. Add feature flag in developer options which is default disabled.

Bug: 111861907
Bug: 118470430
Test: Manually test the flow
Test: runtest systemui
Test: atest ImageWallpaperTransformerTest
Test: atest AodMaskViewTest

Change-Id: Iff2642d52264e88012f4759842a59aaf5bc45b38