Show sth like `Syncing` instead of `No Notes` right after login

### What
As mentioned in p5T066-2Co-p2#comment-9776, at the moment of login the note list will show `No Notes` with a spinning wheel below:

https://user-images.githubusercontent.com/73365754/131475314-cf95446b-eba0-4fd3-9f49-889334a58b69.mov

It would be less frightening if it said something like `Syncing` during this time.

### Why
It will make the experience less stressfully.

Start by locating the macOS note list and the login-time loading state that currently displays “No Notes” with a spinner. Done means the list shows a syncing message during post-login synchronization and returns to the normal empty-state message when synchronization completes.

Written by the indexing model from the issue text.