[SysUI][Floaty] Add top level zoom API to AppZoomOut

Adds a setTopLevelScale API function to AppZoomOut which zooms out all
surfaces on the screen belonging to FEATURE_WINDOWED_MAGNIFICATION.

Bug: 399263897
Test: AppZoomOutControllerTest
Test: Manual, i.e. verified scale is applied to all affected surfaces.
      Also verified that the scale only has to be applied on one parent
      surface.
Flag: com.android.systemui.shared.enable_lpp_assist_invocation_effect
Change-Id: Icbabaccd7e46fc4a3076e3ddbdd7fc2060aa78c4