devdraw: handle windowDidResize on macOS (#212)

This supports non-live window resize.

src/cmd/devdraw/cocoa-screen-metal.m

@@ -342,6 +342,13 @@ struct Cursors {
 	return YES;
 }
 
+- (void)windowDidResize:(NSNotification *)notification
+{
+	if(![myContent inLiveResize] && img) {
+		resizeimg();
+	}
+}
+
 - (void)windowDidBecomeKey:(id)arg
 {
         [myContent sendmouse:0];
@@ -1112,7 +1119,6 @@ resizewindow(Rectangle r)
 
 		s = [myContent convertSizeFromBacking:NSMakeSize(Dx(r), Dy(r))];
 		[win setContentSize:s];
-		resizeimg();
 	});
 }