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/core-js/internals/inherit-if-required.js

@@ -0,0 +1,19 @@
+'use strict';
+var isCallable = require('../internals/is-callable');
+var isObject = require('../internals/is-object');
+var setPrototypeOf = require('../internals/object-set-prototype-of');
+
+// makes subclassing work correct for wrapped built-ins
+module.exports = function ($this, dummy, Wrapper) {
+  var NewTarget, NewTargetPrototype;
+  if (
+    // it can work only with native `setPrototypeOf`
+    setPrototypeOf &&
+    // we haven't completely correct pre-ES6 way for getting `new.target`, so use this
+    isCallable(NewTarget = dummy.constructor) &&
+    NewTarget !== Wrapper &&
+    isObject(NewTargetPrototype = NewTarget.prototype) &&
+    NewTargetPrototype !== Wrapper.prototype
+  ) setPrototypeOf($this, NewTargetPrototype);
+  return $this;
+};