LibWeb/HTML: Implement TextTrackCueList idl interface

Author: https://github.com/jamierocks
Commit: cfec88feb3
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/1494
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/tcl3 ✅

Userland/Libraries/LibWeb/Forward.h

@@ -497,6 +497,7 @@ class SubmitEvent;
 class TextMetrics;
 class TextTrack;
 class TextTrackCue;
+class TextTrackCueList;
 class TextTrackList;
 class Timer;
 class TimeRanges;