Move fullscreen tasks with move-to-next-display shortcut

This CL enables the move-to-next-display shortcut to work with
fullscreen tasks, in addition to desktop (freeform) tasks. This commit
specifically focuses on changing DesktopModeKeyGestureHandler so that it
can pick fullscreen task for devices in projected mode.

When the user activates the shortcut, the system will now check for a
focused fullscreen task if no desktop task is focused. This allows
moving a fullscreen app from a projected display to another display.

This behavior is gated by the
`move_to_next_display_shortcut_with_projected_mode` flag.

Bug: 424748132
Test: DesktopModeKeyGestureHandlerTest
Flag: com.android.window.flags.move_to_next_display_shortcut_with_projected_mode
Change-Id: I232e7e28aefb51301f057a78f4d39c14120e53f7