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-pure/modules/esnext.async-iterator.from.js

@@ -0,0 +1,18 @@
+'use strict';
+var $ = require('../internals/export');
+var toObject = require('../internals/to-object');
+var isPrototypeOf = require('../internals/object-is-prototype-of');
+var getAsyncIteratorFlattenable = require('../internals/get-async-iterator-flattenable');
+var AsyncIteratorPrototype = require('../internals/async-iterator-prototype');
+var WrapAsyncIterator = require('../internals/async-iterator-wrap');
+
+// `AsyncIterator.from` method
+// https://github.com/tc39/proposal-async-iterator-helpers
+$({ target: 'AsyncIterator', stat: true, forced: true }, {
+  from: function from(O) {
+    var iteratorRecord = getAsyncIteratorFlattenable(typeof O == 'string' ? toObject(O) : O);
+    return isPrototypeOf(AsyncIteratorPrototype, iteratorRecord.iterator)
+      ? iteratorRecord.iterator
+      : new WrapAsyncIterator(iteratorRecord);
+  }
+});