FRE-600: Fix code review blockers

- Consolidated duplicate UndoManagers to single instance
- Fixed connection promise to only resolve on 'connected' status
- Fixed WebSocketProvider import (WebsocketProvider)
- Added proper doc.destroy() cleanup
- Renamed isPresenceInitialized property to avoid conflict

Co-Authored-By: Paperclip <noreply@paperclip.ing>

node_modules/core-js/modules/esnext.array.unique-by.js

@@ -0,0 +1,12 @@
+'use strict';
+var $ = require('../internals/export');
+var addToUnscopables = require('../internals/add-to-unscopables');
+var uniqueBy = require('../internals/array-unique-by');
+
+// `Array.prototype.uniqueBy` method
+// https://github.com/tc39/proposal-array-unique
+$({ target: 'Array', proto: true, forced: true }, {
+  uniqueBy: uniqueBy
+});
+
+addToUnscopables('uniqueBy');