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/internals/advance-string-index.js

@@ -0,0 +1,8 @@
+'use strict';
+var charAt = require('../internals/string-multibyte').charAt;
+
+// `AdvanceStringIndex` abstract operation
+// https://tc39.es/ecma262/#sec-advancestringindex
+module.exports = function (S, index, unicode) {
+  return index + (unicode ? charAt(S, index).length : 1);
+};