LibWeb: Implement MediaCapabilities.decodingInfo()

Author: https://github.com/Psychpsyo
Commit: 0206697d36
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3548
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/Lubrsi
Reviewed-by: https://github.com/shannonbooth

Libraries/LibWeb/HTML/EventLoop/Task.h

@@ -71,6 +71,9 @@ public:
         // https://websockets.spec.whatwg.org/#websocket-task-source
         WebSocket,
 
+        // https://w3c.github.io/media-capabilities/#media-capabilities-task-source
+        MediaCapabilities,
+
         // !!! IMPORTANT: Keep this field last!
         // This serves as the base value of all unique task sources.
         // Some elements, such as the HTMLMediaElement, must have a unique task source per instance.