Add API windowSplashScreenIconBackground(12/N)

Add new API for developer to customize starting window, set a
background color behind the icon.

Also masking the AVD and icon background like AdaptiveIconDrawable.

Ref doc: go/improved_app_launch_animations

Bug: 73289295
Test: atest SplashscreenTests
Change-Id: Ibba49ecc3ca020022cf775fed302e383908be327