[flexiglass] Fixes issue where collapsing the shade went to AOD

The issue was that LockscreenSceneTransitionInteractor's
nextLockscreenTargetState wasn't being reset to LOCKSCREEN when we left
the Lockscreen scene so the lingering AOD would be picked back up when
returning to the Lockscreen scene, causing KTF to return to AOD.

The fix still works for Shade -> Lockscreen (in AOD) when pressing the
power button while on the Shade scene because the call to
changeScene(Lockscreen) also carries with it an AOD sceneState parameter
which means that LockscreenSceneTransitionInteractor picks that up in
its startTransitionToLockscreen method and correctly shifts LS to AOD.

Fix: 395063194
Test: manually verified that collapsing the shade on top of a locked
device correctly ends up in the Lockscreen scene in the LOCKSCREEN state
(not AOD)
Test: manually verified that pressing the power button while on the
shade (on top of a locked or unlocked device) correctly ends up in the
Lockscreen scene in the AOD state
Flag: com.android.systemui.scene_container

Change-Id: I0bfa5b7515bfe8b96191b95c25d97f98e07a2a29