Default-to-desktop based on the state of desktop first

This CL consolidates default-to-desktop with desktop-first.
Default-to-desktop is no longer a per-device preference but the
universal connected display policy.

Bug: 406608393
Test: atest DesktopTasksControllerTest
Flag: com.android.window.flags.enable_desktop_first_based_default_to_desktop_bugfix
Change-Id: I8d462d7c977236fd5554f9cf62256153019b6146