Enable joystick events in background

Capture the gamepads even when the window is not focused.

Note: In theory, with this flag set, we could capture gamepad events
even without a window (--no-window). In practice, scrcpy still requires
a window, because --no-window implies --no-control, and the input
manager is owned by the sc_screen instance, which does not exist if
there is no window. Supporting this use case would require a lot of
refactors.

Refs <https://github.com/Genymobile/scrcpy/pull/5270#issuecomment-2339360460>
PR #5270 <https://github.com/Genymobile/scrcpy/pull/5270>

Suggested-by: Luiz Henrique Laurini <luizhenriquelaurini@gmail.com>