Fix file finder menu actions (#21087)

Closes https://github.com/zed-industries/zed/issues/21077

* BREAKING: rename `file_finder::OpenMenu` into
`file_finder::ToggleMenu`
* Display the keybinding for menu toggling when the menu is open
* Fix `enter` not working in the menu

Release Notes:

- Fixed enter not working and menu toggle binding not shown in the file
finder menu