[css-font-loading-3] Align with Web IDL specification (w3c#4797)

Author: autokagami

css-font-loading-3/Overview.bs

@@ -95,7 +95,7 @@ The <code>FontFace</code> Interface</h2>
 		[Exposed=(Window,Worker)]
 		interface FontFace {
 			constructor(CSSOMString family, (CSSOMString or BinaryData) source,
-		                optional FontFaceDescriptors descriptors);
+		                optional FontFaceDescriptors descriptors = {});
 			attribute CSSOMString family;
 			attribute CSSOMString style;
 			attribute CSSOMString weight;
@@ -437,7 +437,7 @@ The <code>FontFaceSet</code> Interface</h2>
 
 		[Exposed=(Window,Worker)]
 		interface FontFaceSetLoadEvent : Event {
-			constructor(CSSOMString type, optional FontFaceSetLoadEventInit eventInitDict);
+			constructor(CSSOMString type, optional FontFaceSetLoadEventInit eventInitDict = {});
 			[SameObject] readonly attribute FrozenArray<FontFace> fontfaces;
 		};