Don't install a pointer input when there are no user actions

This CL checks whether our swipeToScene() modifiers should be enabled
during composition (instead of during gesture, prior to this CL) so that
gestures will pass through a SceneTransitionLayout when there is no user
actions defined on the current scene.

Bug: 370913106
Test: atest SwipeToSceneTest
Flag: com.android.systemui.scene_container
Change-Id: I77e2fa7a57ad367ab7a405ba53ee5511f98ba848