Library conflicts prompted #31148 (MR51: Allow Matplotlib to use system qhull >= 7.2.0).

We should also allow our optional package qhull to find system qhull; and upgrade it on the way.

With #31580 qhull is promoted to standard.

CC: @zlscherr @jhpalmieri @dimpase @antonio-rojas @orlitzky @mkoeppe

Component: packages: standard

Keywords: upgrade, qhull

Author: Samuel Lelièvre, Dima Pasechnik

Branch/Commit: e073d08

Reviewer: John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/31161