Move home task to back on core launch

In some launches, e.g gmail compose from taskbar, the intent has the
flag TASK_ON_HOME. This flag moves the home task behind the task being
launched. In desktop mode, we don't want this to happen so move home to
back when shell handles this launch.

Bug: 341753779
Test: atest DesktopTasksControllerTest
Flag: EXEMPT bugfix
Change-Id: I14714e7c19cf602864f83436af8d71b9cd5adfc1