bug#71419: 30.0.50; Completion does not always highlight the "common part" corresponding to suffix

[Stefan Monnier]

> For example:
>
> 1. Type (fo|-function
> 2. C-M-i
>
> You get 5 completions (the exact number is not important), where "fo" is
> highlighted in all of them, but "function is not.

Looks like a bug in the `basic` completion style: it filters things that
match the glob pattern `fo*-function` yet it only highlights the prefix.

> Also, highlighting is information. If it was more uniform, we could use
> it to e.g. address the FIXME in completion-all-completions.

I don't think it could be trusted to always provide the needed data (and
even if it does, it would be sufficiently clunky to use that I'm not
sure we'd want to rely on it).


        Stefan