FIX: Add a 0-length timer to allow fast animations to redraw on macosx

The macosx backend would not update on flush_events calls due to the
loop being run too fast for the view to update properly in the NSApp.
Fix that by adding an unnoticeable RunLoop timer slowdown that
allows the app to see the changes.

Author: greglucas

src/_macosx.m

@@ -354,6 +354,9 @@ static CGFloat _get_device_scale(CGContextRef cr)
 static PyObject*
 FigureCanvas_flush_events(FigureCanvas* self)
 {
+    // We need to allow the runloop to run very briefly
+    // to allow the view to be displayed when used in a fast updating animation
+    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.0]];
     [self->view displayIfNeeded];
     Py_RETURN_NONE;
 }