screen capture: add resize handlers

From spec, add 4 resize handlers on the 4 corners of the region box and
hide the resize handlers during moving or resizing the region box.

Bug: 439660708, 423963391
Test: Manual
Flag: com.android.systemui.large_screen_screencapture

Change-Id: Ie203d2199a9741e4d528df48c56032543f5c7a13