Add loading attribute for img and iframe

Author: pete-murphy

codegen/consts.js

@@ -50,6 +50,7 @@ module.exports.types = {
   "formNoValidate": "Boolean",
   "hidden": "Boolean",
   "itemScope": "Boolean",
+  "loading": "String",
   "loop": "Boolean",
   "maxLength": "Int",
   "minLength": "Int",

codegen/react-html-attributes.json

@@ -282,6 +282,7 @@
   ],
   "iframe": [
     "height",
+    "loading",
     "name",
     "sandbox",
     "scrolling",
@@ -291,6 +292,7 @@
   "img": [
     "alt",
     "height",
+    "loading",
     "name",
     "sizes",
     "src",