Force enter desktop mode on secondary display

From go/desktop-first-eng, this should always be the case.

Fix: 403506870
Test: atest DesktopTasksControllerTest
Flag: com.android.window.flags.enter_desktop_by_default_on_freeform_displays
Change-Id: Id56444e3358dcb3670adfa5b751e1aeebd6e2d0c