Split up KeyguardBottomArea

This splits the KeyguardBottomArea into many pieces:
- Left shortcut
- Right shortcut
- Ambient indication container
- Customize Lockscreen button

Each of the elements above are now able to be independently laid out.

The alpha of the entire KeyguardRootView can now be easily modified, rather than having to adjust the alpha of each sub-element individually.

Fixes: 278057014
Test: atest KeyguardQuickAffordancesCombinedViewModelTest.kt
Test: atest KeyguardRootViewModelTest.kt
Change-Id: I098174809144cdf09dd71665ab724f8c508ae9e9