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.set.union.v2.js

@@ -0,0 +1,13 @@
+'use strict';
+var $ = require('../internals/export');
+var union = require('../internals/set-union');
+var setMethodGetKeysBeforeCloning = require('../internals/set-method-get-keys-before-cloning-detection');
+var setMethodAcceptSetLike = require('../internals/set-method-accept-set-like');
+
+var FORCED = !setMethodAcceptSetLike('union') || !setMethodGetKeysBeforeCloning('union');
+
+// `Set.prototype.union` method
+// https://tc39.es/ecma262/#sec-set.prototype.union
+$({ target: 'Set', proto: true, real: true, forced: FORCED }, {
+  union: union
+});