Move task to fullscreen on startLockTaskMode.

When a transition starts to enter lock task mode, move the task to
fullscreen. To do that with desks, we need to enable reparenting
operations during lock task.

Bug: 402443859
Test: Manual using TestDPC & atest DesktopTasksControllerTest
Flag: com.android.window.flags.enable_desktop_windowing_enterprise_bugfix
Change-Id: I632416c82cb4da969dd027a1abe88a91f227da2b