Add a new transition type for lock task mode

Add TRANSIT_START_LOCK_TASK_MODE to be used when starting lock task
mode. This allows shell to identify when a lock task mode is happening
and add any presentation changes.

Bug: 402443859
Test: Manual using TestDPC
Flag: com.android.window.flags.enable_desktop_windowing_enterprise_bugfix
Change-Id: Ic9356e707d500939b8071cfa8df760d37ad32e7b