Tablet mode signal-based desktop-first switch

This CL lets the controller use a tablet mode signal to determine the
display windowing mode.
If a tablet mode is explicitly disabled, the device goes to
desktop-first mode.

Flag: com.android.window.flags.form_factor_based_desktop_first_switch
Bug: 400645972
Test: DesktopDisplayModeControllerTest
Change-Id: I0d0995bb985b830aa529e712aa1cb9c16e2262f5