Make flexiglass window visible when swiping on launcher and status bar

When a touch is going to be proxied from launcher to shade, the flexiglass
window is made visible so touches can slip onto it. Touches on the status
bar are piped into flexiglass through SceneInteractor. Both invocation
methods open the shade scene directly at the moment, awaiting various blockers.

Bug: 290682366
Test: new unit test
Test: manually verified MotionEvents being detected in flexiglass from swipes
on launcher and status bar
Test: manually verified no behavior is changed when the feature flag is disabled

Change-Id: I0feb4b5b38f3bf00ac846e9bba735dbeff145f3c