Use getStableBounds if we are in desktop mode

Don't use getStableBoundsForDesktopMode as it can be incorrect if insets
were updated in runtime. If already in desktop mode, getStableBounds
should return correct insets.

Flag: EXEMPT bug fix
Bug: 406182386
Test: atest DesktopTasksControllerTest
Change-Id: Iea0110cef8027b684b4c5d45f97d9a1e68d37af3