Align with Web IDL change: [LenientSetter] → [LegacyLenientSetter]

Follows whatwg/webidl#870.

Author: domenic

fullscreen.bs

@@ -174,8 +174,8 @@ partial interface Element {
 };
 
 partial interface Document {
-  [LenientSetter] readonly attribute boolean fullscreenEnabled;
-  [LenientSetter, Unscopable] readonly attribute boolean fullscreen; // historical
+  [LegacyLenientSetter] readonly attribute boolean fullscreenEnabled;
+  [LegacyLenientSetter, Unscopable] readonly attribute boolean fullscreen; // historical
 
   Promise<void> exitFullscreen();
 
@@ -184,7 +184,7 @@ partial interface Document {
 };
 
 partial interface mixin DocumentOrShadowRoot {
-  [LenientSetter] readonly attribute Element? fullscreenElement;
+  [LegacyLenientSetter] readonly attribute Element? fullscreenElement;
 };
 </pre>
 <!-- The event handler attributes are intentially not in a partial DocumentAndElementEventHandlers