[flexiglass] Prevent user actions from changing to Gone when locked

We already had in place a protection for programmatic scene changes in
SceneInteractor#validateSceneChange; this protects calls to changeScene
and snapToScene. We didn't have protection for a user action being
mapped to Gone inside of whatever the current scene is (this would be a
bug, not user error, but alas).

This CL adds protection against switching to Gone while the device is
still locked following a user action. For example, if the Lockscreen
scene has a logical bug where swiping up on it switches to the Gone
scene regardless of unlock state, this protection will catch that and
stop it from happening.

Fix: 425987992
Test: unit tests modified and added
Test: temporarily introduced a bug where swiping up on the Lockscreen
scene always went to Gone. Verified that this would be allowed without
the fix and not allowed after the fix
Flag: com.android.systemui.scene_container

Change-Id: I94171e2b95454a8a62f32c145807f6fec80399e6