MM-21898 - Part 1: Generate and use an interface instead of *A… (#13840)

* Generate and use an interface instead of *App

wsapi/user.go

@@ -13,7 +13,7 @@ func (api *API) InitUser() {
 }
 
 func (api *API) userTyping(req *model.WebSocketRequest) (map[string]interface{}, *model.AppError) {
-	if api.App.Srv.Busy.IsBusy() {
+	if api.App.Srv().Busy.IsBusy() {
 		// this is considered a non-critical service and will be disabled when server busy.
 		return nil, NewServerBusyWebSocketError(req.Action)
 	}