[7/n] Add parentTaskId for persisted tasks after reboot

Set launchRootTask for task in background which will be relaunched in
desk after device reboot. This ensures taskInfo.parentTaskId will be set
to the correct deskId instead of -1.

Flag: EXEMPT bug fix
Test: atest DesktopTasksControllerTest
      atest RootTaskDesksOrganizerTest
Bug: 423560267
Change-Id: I86dad3b208ac49426f132f61e1897a6c756a998f