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/es.object.assign.js

@@ -0,0 +1,10 @@
+'use strict';
+var $ = require('../internals/export');
+var assign = require('../internals/object-assign');
+
+// `Object.assign` method
+// https://tc39.es/ecma262/#sec-object.assign
+// eslint-disable-next-line es/no-object-assign -- required for testing
+$({ target: 'Object', stat: true, arity: 2, forced: Object.assign !== assign }, {
+  assign: assign
+});