[SceneContainer] Fix touchable area when a HUN is displayed

When a HUN is shown sceneContainer would be set to visible, which would
hard set the touchable area to the entire screen in
`StatusBarTouchableRegionManager`. This fix now instead observes the
scene transition state instead and sets the touchable area to full
screen on all scenes except for Gone. While on Gone the touchable area
is determined by the region where a HUN is shown.

There is currently a different bug for some edge cases in
`getTouchableRegion()` that is now tracked in b/347007367.

Bug: 343688970
Flag: com.android.systemui.scene_container
Test: Manual tests
Change-Id: I9deb003df3dcf5c90d96666124e62c73cdbc1c23