LibWeb: Add ImageData objects and implement 2D context putImageData()

An ImageData is a wrapper around a Bitmap wrapper around a
JS::Uint8ClampedArray.

Libraries/LibWeb/Forward.h

@@ -42,6 +42,7 @@ class HTMLHeadElement;
 class HTMLHtmlElement;
 class HTMLImageElement;
 class HtmlView;
+class ImageData;
 class LayoutDocument;
 class LayoutNode;
 class MouseEvent;
@@ -64,6 +65,7 @@ class EventListenerWrapper;
 class EventTargetWrapper;
 class HTMLCanvasElementWrapper;
 class HTMLImageElementWrapper;
+class ImageDataWrapper;
 class MouseEventWrapper;
 class NodeWrapper;
 class WindowObject;