app: add Window.Raise to bring a window to the front

Fixes gio#252

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

app/os_macos.go

@@ -127,6 +127,12 @@ static CFTypeRef layerForView(CFTypeRef viewRef) {
 	NSView *view = (__bridge NSView *)viewRef;
 	return (__bridge CFTypeRef)view.layer;
 }
+
+static void raiseWindow(CFTypeRef windowRef) {
+	NSWindow* window = (__bridge NSWindow *)windowRef;
+	[window makeKeyAndOrderFront:nil];
+}
+
 */
 import "C"
 
@@ -268,6 +274,10 @@ func (w *window) SetAnimating(anim bool) {
 	}
 }
 
+func (w *window) Raise() {
+	C.raiseWindow(w.window)
+}
+
 func (w *window) runOnMain(f func()) {
 	runOnMain(func() {
 		// Make sure the view is still valid. The window might've been closed