LibWeb: Implement HTMLCanvasElement.toBlob()

Author: https://github.com/krkk
Commit: b731705fec
Pull-request: https://github.com/SerenityOS/serenity/pull/20341
Reviewed-by: https://github.com/kennethmyhra

Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.h

@@ -34,6 +34,7 @@ public:
     WebIDL::ExceptionOr<void> set_height(unsigned);
 
     DeprecatedString to_data_url(DeprecatedString const& type, Optional<double> quality) const;
+    WebIDL::ExceptionOr<void> to_blob(JS::NonnullGCPtr<WebIDL::CallbackType> callback, DeprecatedString const& type, Optional<double> quality);
 
     void present();