devel/py-breathe: RST&Sphinx bridge to Doxygen [backport]

This combines three commits to avoid the bulk of larger files.

Breathe provides a bridge between the Sphinx and Doxygen documentation systems.

It is an easy way to include Doxygen information in a set of documentation
generated by Sphinx. The aim is to produce an autodoc like support for people
who enjoy using Sphinx but work with languages other than Python. The system
relies on the Doxygen’s xml output.

WWW: https://github.com/michaeljones/breathe

(cherry picked from commit 7fc9eb511a9de8d22aadc855b2812208e04f7b35)
(cherry picked from commit 47570d5b3c9b646a2b17ef9b4a28e52e21e4c48c)
(cherry picked from commit 7c2762b3f43341c1f9822c3ee3634f5ddf5a4d8d)