WindowServer: Make hit test results richer

Instead of just answering hit/no-hit when hit testing windows, we now
return a HitTestResult object which tells you which window was hit,
where it was hit, and whether you hit the frame or the content.

Userland/Services/WindowServer/HitTestResult.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/WeakPtr.h>
+#include <LibGfx/Point.h>
+
+namespace WindowServer {
+
+class Window;
+
+struct HitTestResult {
+    WeakPtr<Window> window;
+    Gfx::IntPoint screen_position;
+    Gfx::IntPoint window_relative_position;
+    bool is_frame_hit { false };
+};
+
+}