[flexiglass] When occluded, swiping down always goes to shade.

It doesn't go to QS, even if swiping down from the edge and even if
swiping down with two fingers.

Fix: 379843374
Test: unit test cases added before coding, coded until green (TDD)
Test: manually verified using double-tap power to occlude the lockscreen
with the camera app and then swipe down with one and with two fingers -
it always opened the shade scene and never QS
Test: made sure that edge and two finger swipe down does go to QS when
not occluded and as expected (no harm testing)
Flag: com.android.systemui.scene_container

Change-Id: Idc714fa678d5c1a99a2e958fb991336fb237c68f