[SysUI][Floaty] Move TopLevelWindowEffects window to a separate thread

Bug: 411041510
Flag: com.android.systemui.shared.enable_lpp_assist_invocation_effect
Test: manual, tested the entire feature with window on separate thread,
seems to be working correctly

Change-Id: Ie8d046b46f5bac815e464720f46bf81bcd3f93b0