Floating menu repositions on navigation mode change

Forces a position update when nav mode changes,
so that if the navBar appears or disappears the FAB moves appropriately

Demonstration video: https://x20web.corp.google.com/users/jo/jonesriley/fabFootage/fabNavModeFix.mp4

Bug: 360030334
Test: atest com.android.systemui.accessibility.floatingmenu
Flag: EXEMPT small internal change
Change-Id: I338b30a6a5d0d4882c4ea8300d13c32f36cc238c