left-align preview window to the right of the finder

[ddickstein]

Checklist

• [X] I have read through the manual page (man fzf)
• [X] 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

0.23.0

OS

• [X] Linux
• [ ] macOS
• [ ] Windows
• [ ] Etc.

Shell

• [X] bash
• [ ] zsh
• [ ] fish

Problem / Steps to reproduce

Currently if I left-align the preview window, it appears first (on the left), followed by the finder. If I right-align it, it appears all the way on the right, which may be far away from the finder in the case of a large number of columns (and a fixed-width preview window). I'd like to have a way to have it appear on the right of the finder, but as close as possible to it (i.e. leftmost viable position without clobbering text from finder options). I can think of a couple possibilities here:

1. If running with --sync, examine the string lengths of all the options and place the preview window just after the longest.
2. Simpler, let users say the preview window should be left-aligned, but offset by N columns, which gives space for the finder window. Let users figure out an appropriate value for N based on the expected input lengths.

[LangLangBart]

I'd like to have a way to have it appear on the right of the finder, but as close as possible to it

Possible duplicate of #3570