Show completions' `ToolTip` as `--preview`

[cspotcode]

Would be nice to see CompletionMatches' .ToolTips in the fzf --preview-window.

Here's how I think this could work:

• get array of completions
• Generate JSON object: keys == CompletionText, values == ToolTip
• Write JSON to a temp file
• pass a command to fzf --preview that can lookup a value from a key in the JSON
  • If using jq, could be: fzf --preview 'jq --raw-output --arg key "{1}" ".[$key]" /path/to/tempfile.json'
  • relying on an external binary is not ideal
  • fzf might get support for reading directly from JSON, no need for external jq binary

[cspotcode]

Asked fzf about feasibility of adding a --preview mechanism that reads all previews as structured data, either via stdin or from a temp file: junegunn/fzf#4601

[kelleyma49]

I have thought about doing something like this in the past, but I couldn't think of an elegant way to save the tooltip state and reference it in the preview window.

[cspotcode]

How do you feel about my JSON temp file idea? Or a temp file format that's more friendly to being parsed by a simple sh-compatible shell?