Migrating some files from javascript to typescript (#24663)

* Migrating some files to typescript

* Some other files migrated

* Migrating more javascript to typescript

* Migrating more javascript to typescript

* Fixing types

* Fixing linter errors

* Fixing some imports

* Fixing linter errors

* Renaming the snapshots

* Addressing PR review comments

webapp/channels/src/client/web_websocket_client.tsx

@@ -3,5 +3,5 @@
 
 import {WebSocketClient} from '@mattermost/client';
 
-var WebClient = new WebSocketClient();
+const WebClient = new WebSocketClient();
 export default WebClient;