System UI: add box dragging capability to region box for screen capture

the box is bound to the boundaries of the screen.

Screen Record: http://shortn/_GN7nGPBdzn

Bug: 417533251
Test: Manual
Flag: com.android.systemui.desktop_screen_capture
Change-Id: Icf2e219d7d1f195fa6bdbdac6c064bf05d5a08af