Fix cursor blinking not working (#13130)

This was a bug in https://github.com/zed-industries/zed/pull/12990, due
to the new focus restoration logic introduced with the editor.

With this pull request, the editor will only restore focus when a
descendant lost it. If the focus was lost by the editor itself, there's
no need to restore it and we can instead proceed with starting the
cursor blink.

Release Notes:

- N/A