Implement DPI Usability Upgrades for X11 and Wayland (#1098)

* Fix compile errors

* Use `mio` for the X11 event loop

* Removes `calloop` from the X11 event loop, as the method of draining a
  source using a closure provided to the `calloop::EventLoop` instance
  conflicts with the need to deliver events directly to the callback
  provided to `EventLoop::run`, in order to respond to the value provided by
  `WindowEvent::HiDpiFactorChanged`.

* Implement interactive `HiDpiFactorChanged` event for X11

* Implement interactive `HiDpiFactorChanged` event for Wayland

* Run cargo fmt

* Fix Wayland not processing events from EventQueue

* Backport #981

src/platform_impl/linux/wayland/mod.rs

@@ -2,10 +2,7 @@
            target_os = "netbsd", target_os = "openbsd"))]
 
 pub use self::{
-    event_loop::{
-        EventLoop, EventLoopProxy, EventLoopWindowTarget, MonitorHandle, VideoMode,
-        WindowEventsSink,
-    },
+    event_loop::{EventLoop, EventLoopProxy, EventLoopWindowTarget, MonitorHandle, VideoMode},
     window::Window,
 };