Add lin.el for dynamic hl-line in different contexts

### Describe your request

The great Protesilaos Stavrou has [recently introduced](https://protesilaos.com/codelog/2021-11-01-introducing-lin/) lin.el (*LIN Is Noticeable*) which "[...] remaps `hl-line` face buffer-locally to a style that is optimal for major modes where line selection is the primary mode of interaction."

This is especially useful for all sorts of selection/search buffers (ivy/vertico/helm/ido) that current suffer from bad `hl-line` colors.

Prot intends to submit `lin.el` to GNU ELPA "[...] sometime before the 10th of November".

### Briefly explain its use-case

A quote from [the manual](https://protesilaos.com/emacs/lin):

> The idea is that hl-line cannot work equally well for contexts with competing priorities: (i) line selection, or (ii) simple line highlight. In the former case, the current line needs to be made prominent because it carries a specific meaning of some significance in the given context. Whereas in the latter case, the primary mode of interaction does not revolve around the line highlight itself: it may be because the focus is on editing text or reading through the buffer’s contents, so the current line highlight is more of a gentle reminder of the point’s location on the vertical axis.

There is a pretty good example in the introduction blog post linked above that *highlights* the use-case: