[Dual Shade] Separate the notifications and QS shades for transitions.

For the time being, it's decided to not have a shared element transition
when transitioning between the two shades.

BONUS: Fade the shade header (aka shade status bar) during the
transition.

Fix: 391151101
Bug: 394149273
Test: Manually by expanding and collapsing the shades over Lockscreen
 and verifying there's no shared element transition between them.
Flag: com.android.systemui.scene_container
Change-Id: I40b1dea47fa4d6fc85bf5b21a064305e2ea05734