Closes https://github.com/zed-industries/community/issues/1095
by forcing the non-Cancel button to get a focus.
Due to the way macOs handles buttons on modals, the focus gain had to be
achieved via certain button addition order, rather than conventional
"setFocus"-ish API, see the related comment for details.

Co-authored-by: Antonio Scandurra <antonio@zed.dev>