Replace xrandr processes with FFI libxrandr calls

[srithon]

The overhead of spawning processes has become even more apparent with the multi-monitor fix. Rather than tuning down the fades, I feel that if we interface with the libxrandr C API instead of using the xrandr executable, the performance will improve.

[srithon]

The gdk crate looks like it covers a lot of what we need, but it will require more research. It lets us get information from the display, but we still need to rely on xrandr to set brightness.

NOTE: I still have to see if we can use any of this without creating a window

Here are the highlights of the crate. We could use this to see which monitor the mouse is currently on

gdk::DisplayManager

• DisplayManager::get()
  • gets the singleton DisplayManager object
• list_displays
  • gives you a Vec<Display>

gdk::Display

• Display::get_default()
  • alternative to using DisplayManager::get() intermediate
• connect_monitor_added
  • lets us set callbacks for when monitors are connected (add to enabled_monitors)
• connect_monitor_removed
  • lets us set callbacks for when monitors are disconnected (remove from enabled_monitors)
• get_monitor_at_point
  • lets you see which monitor a point is on
• get_device_manager -> Option<DeviceManager>
• get_default_seat -> Option<Seat>
• get_screen -> Screen

gdk::DeviceManager Phased out for gdk::Seat

gdk::Seat

• get_pointer -> Option<Device>
  • gets the mouse pointer

gdk::Device

• get_position -> (Screen, i32, i32)
  • gets the mouse cursor position (if the Device is a mouse)

gdk::Screen

• get_active_window -> Option<Window>
  • use this to get which window is focused
  • NOTE: this is deprecated, so we either need to accept that and use it OR find an alternative