vim: set cursor to hollow-block if editor loses focus (#10995)

This has been bugging me for a while now. Finally figured out how to do
it.

Release Notes:

- Fixed cursor in Vim mode not changing into a hollow block when editor
loses focus.


Demo: 


https://github.com/zed-industries/zed/assets/1185253/c7585282-156d-4ab2-b516-eb1940d6d0d3