[flexiglass] Make sure scene and userActions are in-sync

Makes sure that the userActions map used for each scene matches that
scene exactly. Before this CL, there was a chance that the current scene
inside STL and the current scene in the scene stack were not the same.
This would cause occasional brief times when the userActions being sent
for the current scene was actually the one for the previous scene; which
caused a crash, by-design, inside of STL when that scene's builder was
called if one of the user actions went to the real current scene.

To make them match, the changes actually go to the real scene object for
each scene key instead of relying on a flow in the scene stack of
classes.

Note that, as a side effect, there's a lot more flow collection now as,
before this change, SceneContainer tried to only collect from the
userActions/sceneDestinations flow of the current scene. This CL changes
that to always collect from the flows of all scenes - which is
unfortunate but not clear that it creates performance issues.

Perhaps if we change the userActions parameter of the scene builder in
STL to allow for lazy / provider instead of a direct read it will reduce
performance impact.

Fix: 349430360
Test: manually verified that the original crash from the bug doesn't
happen anymore
Test: manually smoked-tested many scene transitions on locked and
unlocked device (shade and QS over lockscreen, bouncer, unlock, shade
and QS over gone, re-lock, shade and QS) also display on and off
Flag: com.android.systemui.scene_container

Change-Id: I1348b3aa22090c435bb246fd5e82517a0c32cb7c