LibWeb: Implement HTMLMediaElement's duration attribute

Author: https://github.com/trflynn89
Commit: e10e041882
Pull-request: https://github.com/SerenityOS/serenity/pull/18183
Reviewed-by: https://github.com/Lubrsi
Reviewed-by: https://github.com/linusg ✅
Reviewed-by: https://github.com/skyrising

Userland/Libraries/LibWeb/HTML/HTMLMediaElement.idl

@@ -18,16 +18,18 @@ interface HTMLMediaElement : HTMLElement {
     const unsigned short NETWORK_LOADING = 2;
     const unsigned short NETWORK_NO_SOURCE = 3;
     readonly attribute unsigned short networkState;
+    undefined load();
+    CanPlayTypeResult canPlayType(DOMString type);
 
+    // playback state
+    readonly attribute unrestricted double duration;
     [Reflect, CEReactions] attribute boolean autoplay;
     [Reflect, CEReactions] attribute boolean loop;
-
-    [Reflect, CEReactions] attribute boolean controls;
-
-    CanPlayTypeResult canPlayType(DOMString type);
-    undefined load();
     undefined pause();
 
+    // controls
+    [Reflect, CEReactions] attribute boolean controls;
+
     // tracks
     [SameObject] readonly attribute VideoTrackList videoTracks;
 };