Enable 3 desktop mode education hints to launch independently.

Previously desktop mode hints are launched one after the other. This CL
refactors the logic by listening to caption state changes and decides on
which of the hints should be displayed.

Test: atest AppHandleEducationControllerTest
Fixes: 371527084
Flag: com.android.window.flags.enable_desktop_windowing_app_handle_education

Change-Id: Ib9dc6a393b37596252eb5688dd3b3aee779abbb0