I don't know whether there are any hard UI guidelines that dictate
whether this should be allowed or not, but I think it's very handy and
missed it.

I also think it makes sense to have this in a directory-centric editor
in which opening a directory creates a new window.

Release Notes:

- Added ability to create directory in open-file dialog on macOS.

![screenshot-2024-05-22-15 05
03@2x](https://github.com/zed-industries/zed/assets/1185253/939a2a88-16b2-4a91-a344-f73c5615d831)