[FR] add the ability to filter the candidates based on their current line value in fzf

[NightMachinery]

This way, we can use an "easy", general regex, and use some manual, interactive filtering to select just the candidates we need.

To implement this, you only need to add the current line to the choices in fzf, using a separator between the file path and the matched line:

/some/file.txt:the matched line