Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/es-abstract/2019/IsExtensible.js

@@ -0,0 +1,18 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $preventExtensions = GetIntrinsic('%Object.preventExtensions%', true);
+var $isExtensible = GetIntrinsic('%Object.isExtensible%', true);
+
+var isPrimitive = require('../helpers/isPrimitive');
+
+// https://262.ecma-international.org/6.0/#sec-isextensible-o
+
+module.exports = $preventExtensions
+	? function IsExtensible(obj) {
+		return !isPrimitive(obj) && $isExtensible(obj);
+	}
+	: function IsExtensible(obj) {
+		return !isPrimitive(obj);
+	};