[flexiglass] Fixes issue where Flexiglass starts blank.

The issue stemmed from a premature switch to the Gone scene because
canSwipeToEnter started off as false while upstream state was being
collected, triggering the move.

Fix: 312526380
Test: unit tests added
Test: manually verified that after restarting the zygote process, the
system correctly starts on the Lockscreen scene and not the Gone scene
Test: manually verified that unlocking via the bouncer and via face
unlock + with and without bypass still works as expected
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT

Change-Id: I291a9651d29ed5815e8827edad58dcf0b4506b63