screen capture: fix region button box animation lag

The RegionBoxButton and RegionDimensionsPill lagged behind the main
selection box during drag operations. This was due to independent
positioning logic causing their updates to be out of sync with the
main box's graphicsLayer transform.

This change fixes the issue by wrapping the selection box, button,
and pill in a single parent Box that is moved with one
graphicsLayer. This ensures all elements move as a single, atomic
unit, eliminating the visual lag.

Bug: 437192780
Test: Manual
Flag: com.android.systemui.large_screen_screencapture

Change-Id: I268a1b2e344f7ff18539b97970be127d949597fd