Flexiglass, Keyguard: mouse click on empty space should transition to bouncer

This is a reland of ag/34327994 that includes a fix for the
KeyguardTouchHandlingInteractorTest, making sure it correctly works for
both states of the com.android.systemui.scene_container flag.

Test: atest KeyguardKeyEventInteractorTest
Test: atest KeyguardTouchHandlingInteractorTest
Test: manual - enable flexiglass, click on empty space, check that bouncer is shown
Bug: 412922805
Bug: 432709205
Flag: EXEMPT - Feature parity with non-flexiglass code
Change-Id: Ie590e9cc92ab03c7bac99f5fec9265b77596bff3