1. Add [DisplayDeskConfig] when `onDeskAdded` if there is no config yet.
As the display might start without any desks.
2. Trigger the task bar enter or exit on desktop mode changes inside
`onActiveDeskChanged` instead, which is also transition based.
Bug: 408060477
Test: m
Flag: com.android.window.flags.enable_multiple_desktops_frontend
Flag: com.android.window.flags.enable_multiple_desktops_backend
Change-Id: I6f77f2a8d9fe660175b739f44dc241937a6bcc7a
minch
9381184f58