backport fullscreen fix for macOS (#1524)

This backports the recent fullscreen fix for macOS on the master branch to the 5_1-new branch.  Credit goes to GitHub user aeubanks for the original fix.

src/archutils/Darwin/SMMain.mm

@@ -23,7 +23,8 @@
 @implementation SMApplication
 - (void)fullscreen:(id)sender
 {
-	ArchHooks::SetToggleWindowed();
+	// don't use ArchHooks::SetToggleWindowed(), it makes the screen black
+	[[self mainWindow] toggleFullScreen:nil];
 }
 
 - (void)sendEvent:(NSEvent *)event