[multi-shade] Bouncer touch integration.

Connects multi-shade's touch interaction to the bouncer.

On the lock screen such that dragging up when shades are collapsed brings up the bouncer.

https://drive.google.com/file/d/1AiRelfhAg2QFY-EoHvHtG8V6KIzcST_g/view?usp=sharing

Bug: 274159734
Flag: DUAL_SHADE
Test: unit tests expanded for MultiShadeEventInteractor
Test: manually verified that:
1. dragging up when shades are collapsed brings up the bouncer.
2. back gesture hides the bouncer, allowing a drag down to show the dual
   shades again.
3. unlocking the bouncer works as expected.

Change-Id: I81118cb2ccba3bb2887def2568403198e7852c97