On macOS, wake up the event loop immediately when a redraw is requested. (#1812)

We allow to have RunLoop running only on the main thread. Which means if
we call Window::request_redraw() from other the thread then we have to
wait until some other event arrives on the main thread. That situation
is even worse when we have ControlFlow set to the `Wait` mode then user
will not ever render anything.

src/platform_impl/macos/app_state.rs

@@ -25,7 +25,7 @@ use crate::{
     platform_impl::platform::{
         event::{EventProxy, EventWrapper},
         event_loop::{post_dummy_event, PanicInfo},
-        observer::EventLoopWaker,
+        observer::{CFRunLoopGetMain, CFRunLoopWakeUp, EventLoopWaker},
         util::{IdRef, Never},
         window::get_window_id,
     },
@@ -321,6 +321,10 @@ impl AppState {
         if !pending_redraw.contains(&window_id) {
             pending_redraw.push(window_id);
         }
+        unsafe {
+            let rl = CFRunLoopGetMain();
+            CFRunLoopWakeUp(rl);
+        }
     }
 
     pub fn queue_event(wrapper: EventWrapper) {