LibWeb: Add OffscreenCanvas to IDL types

Add OffscreenCanvas to TexImageSource and CanvasImageSource.
Implement all the necessary features to make it work in all cases where
these types are used.

Libraries/LibWeb/WebGL/WebGLRenderingContextBase.h

@@ -6,8 +6,14 @@
 
 #pragma once
 
+#include <LibWeb/Forward.h>
+#include <LibWeb/WebIDL/Types.h>
+
 namespace Web::WebGL {
 
+// NOTE: This is the Variant created by the IDL wrapper generator, and needs to be updated accordingly.
+using TexImageSource = Variant<GC::Root<HTML::ImageBitmap>, GC::Root<HTML::ImageData>, GC::Root<HTML::HTMLImageElement>, GC::Root<HTML::HTMLCanvasElement>, GC::Root<HTML::OffscreenCanvas>, GC::Root<HTML::HTMLVideoElement>>;
+
 // FIXME: This object should inherit from Bindings::PlatformObject and implement the WebGLRenderingContextBase IDL interface.
 //        We should make WebGL code generator to produce implementation for this interface.
 class WebGLRenderingContextBase {

Libraries/LibWeb/WebGL/WebGLRenderingContextOverloads.idl

@@ -4,8 +4,8 @@ typedef (ImageBitmap or
          ImageData or
          HTMLImageElement or
          HTMLCanvasElement or
-         HTMLVideoElement
-         // FIXME: OffscreenCanvas or
+         HTMLVideoElement or
+         OffscreenCanvas
          // FIXME: VideoFrame
          ) TexImageSource;