System UI: Make opposite corners static when dragging on a corner

Each corners of the box is treated separately, and when a corner moves,
we will now manually move the edges of the rectangle.

Screencast: http://shortn/_buldmWsxdu

Bug: 417533606
Test: Manual
Flag: com.android.systemui.desktop_screen_capture
Change-Id: Ica4d3b0eabb89831728f4cd2999872b987b1fd8d