ImageDecoder+LibImageDecoder+LibWeb: Support animations in ImageDecoder

The ImageDecoder service now returns a list of image frames, each with
a duration value.

The code for in-process image decoding is removed from LibWeb, an all
image decode requests are sent out-of-process to ImageDecoder. :^)

This won't scale super well to very long and/or large animations, but
we can work on improving that separately. The main goal here is simply
to stop doing any image decoding inside LibWeb.

Fixes #5165.

Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp

@@ -94,7 +94,7 @@ RefPtr<Layout::Node> HTMLImageElement::create_layout_node()
 
 const Gfx::Bitmap* HTMLImageElement::bitmap() const
 {
-    return m_image_loader.bitmap();
+    return m_image_loader.bitmap(m_image_loader.current_frame_index());
 }
 
 }