Include background task relaunch in isFullscreenRelaunch() filter

This CL removes the visibility check in isFullscreenRelaunch() to let it
include a background fullscreen task.

The expected relaunch consequences are
- Relaunching visible fullscreen task on desktop-first
  -> Keep it fullscreen
- Relaunching invisible fullscreen task on desktop-first
  -> Keep it fullscreen
- Relaunching visible fullscreen task on touch-first
  -> Keep it fullscreen
- Relaunching invisible fullscreen task on touch-first
  -> Change it freeform if any desk is active. Otherwise, keep it
     fullscreen

Flag: com.android.window.flags.enable_desktop_first_fullscreen_refocus_bugfix
Bug: 420499923
Test: DesktopTasksControllerTest
Change-Id: I78e6298a7922d07cf0f7c784173c4c8490a2da5b