Use window corner radius for desktop task snapshots

Desktop task snapshots are shown inside the desktop tile in overview.
They use the window corner radius, when shown on the desktop. Keep the
same radius for the snapshots in overview. Only the desktop tile
background should use the task corner radius.

Bug: 280827930
Flag: persist.wm.debug.desktop_mode_2
Test: open some apps on desktop, swipe up for overview, observe the
      desktop task corner radius remains the same as when on desktop
Change-Id: I55ced9f704b83a6c7619508aa3e7a8080ccc5c35