Everywhere: Use IOSurface as backing store on macOS

Using mmap-allocated memory for backing stores does not allow us to
benefit from using GPU-accelerated painting, because all the performance
increase we get is mostly negated by reading the GPU-allocated texture
back into RAM, so it can be shared with the browser process.

With IOSurface, we get a framebuffer that is both shareable between
processes and can be used as underlying memory for an OpenGL/Metal
texture.

This change does not yet benefit from using IOSurface and merely wraps
them into Gfx::Bitmap to be used by the CPU painter.

Ladybird/WebContent/main.cpp

@@ -148,7 +148,8 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
 #if defined(AK_OS_MACOS)
     if (!mach_server_name.is_empty()) {
-        Core::Platform::register_with_mach_server(mach_server_name);
+        auto server_port = Core::Platform::register_with_mach_server(mach_server_name);
+        WebContent::BackingStoreManager::set_browser_mach_port(move(server_port));
     }
 #endif