vim plugin: support nushell

[Jasha10]

Checklist

• I have read through the manual page (man fzf)
• I have searched through the existing issues
• For bug reports, I have checked if the bug is reproducible in the latest version of fzf

Output of fzf --version

0.56.0 (brew)

OS

• Linux
• macOS
• Windows
• Etc.

Shell

• bash
• zsh
• fish

Problem / Steps to reproduce

I am using nushell, which is not working properly with the fzf vim plugin.

Specifically, the vim systemlist call fzf --version --no-height in is this file is giving an error because the fzf command is passed to shellescape before being passed into systemlist.

Setup:

I have $SHELL == 'User/jasha/.cargo/bin/nu and have set 'shell' and 'shellxquote' to appropriate values.

[Jasha10]

I've created PR #4067 to address this issue.

[KiaraGrouwstra]

c.f. #4122