LibWeb: Add AnimationTimeline IDL object

Author: https://github.com/mattco98
Commit: 521f8bd5f2
Pull-request: https://github.com/SerenityOS/serenity/pull/21801
Reviewed-by: https://github.com/awesomekling ✅

Userland/Libraries/LibWeb/Forward.h

@@ -26,6 +26,10 @@ namespace Web::Painting {
 class RecordingPainter;
 }
 
+namespace Web::Animations {
+class AnimationTimeline;
+}
+
 namespace Web::ARIA {
 class AriaData;
 class ARIAMixin;