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/@sinonjs/commons/lib/class-name.js

@@ -0,0 +1,27 @@
+"use strict";
+
+var functionName = require("./function-name");
+
+/**
+ * Returns a display name for a value from a constructor
+ *
+ * @param  {object} value A value to examine
+ * @returns {(string|null)} A string or null
+ */
+function className(value) {
+    return (
+        (value.constructor && value.constructor.name) ||
+        // The next branch is for IE11 support only:
+        // Because the name property is not set on the prototype
+        // of the Function object, we finally try to grab the
+        // name from its definition. This will never be reached
+        // in node, so we are not able to test this properly.
+        // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name
+        (typeof value.constructor === "function" &&
+            /* istanbul ignore next */
+            functionName(value.constructor)) ||
+        null
+    );
+}
+
+module.exports = className;