Placeholder expression for accept/print actions

[cskeeters]

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

0.55.0

OS

• Linux
• macOS
• Windows
• Etc.

Shell

• bash
• zsh
• fish

Problem / Steps to reproduce

I propose adding placeholder expressions (i.e. {1}) for accept/print actions.

The command:

fzf -d : --with-nth 2.. --bind 'enter:become(echo {1})'

would turn into either:

fzf -d : --with-nth 2.. --bind 'enter:accept({1})'
fzf -d : --with-nth 2.. --bind 'enter:print({1})+abort'

I realize this is a nice to have.

I also think --accept-nth would complement --with-nth and --nth nicely for those users who don't want to mess with bindings and actions or don't understand replacing processes.

fzf -d : --with-nth 2.. --accept-nth 1