Detect EventHandler attributes on interfaces that don't inherit from EventTarget

[dontcallmedom]

This happened at least with WebCodecs (fixed in w3c/webref#874)

[dontcallmedom]

Found another case by reviewing the output of jq '.idlparsed.idlNames[]|select(.type == "interface" and (.members[]|select(.idlType.idlType == "EventHandler")))|(.name + " " + .inheritance)' *.json 2>/dev/null|grep -v EventTarget