LibWeb: Begin implementing media resource seeking

Author: https://github.com/trflynn89
Commit: 5a98a5529f
Pull-request: https://github.com/SerenityOS/serenity/pull/18296
Reviewed-by: https://github.com/Zaggy1024 ✅

Userland/Libraries/LibWeb/HTML/VideoTrack.h

@@ -27,6 +27,7 @@ public:
 
     Time position() const;
     Time duration() const;
+    void seek(Time, MediaSeekMode);
 
     u64 pixel_width() const;
     u64 pixel_height() const;