Enhancement request: `--preview-json` to read previews from a simple key-value object instead of spawning an external process

[cspotcode]

PSFzf uses fzf to power tab-completion menus in PowerShell. Tab completions in PowerShell are rich objects generated in-memory with a few fields:
CompletionText, ListItemText, ResultType, ToolTip

ToolTip often contains useful metadata. For example, for commands, it contains usage information:
Here is a screenshot of PSReadLine's MenuCompletion which shows completion entries as an interactive menu. No fuzzy matching though :( The ToolTip string is the multiline blue text

To expose these tooltips in the preview window, we need to provide a process that can look up each tooltip by name, but all the info is already in-memory. Could there be some way to pass this data structure to fzf either to stdin, or via a temp file referenced by --preview-json-file or similar?