bug#56355: 29.0.50; Implement file-parent-directory

[Eli Zaretskii]

> Date: Sat, 2 Jul 2022 18:06:01 +0700
> From: daanturo <daanturo@gmail.com>
> 
> A way to get the parent directory of a file.
> 
> This is inspired by f.el's f-dirname, but only returns the absolute
> path, also doesn't ignore `file-name-handler-alist`, doesn't strip the
> final "/".

Thanks, but it looks as a very thin wrapper around
file-name-directory, so I wonder whether we really need a separate
function fir this.