WIP: [scout] Platform: Add python3.5
Proton's launch script wants Python 3, and we already have a python3.5 backport for Meson, so we might as well use that more modern version.
Because we aren't installing the default Python 3 version (3.2), this will need to be accompanied by a flatdeb-steam commit (flatdeb-steam!5 (merged)) to set up a /usr/bin/python3 symlink.
https://phabricator.collabora.com/T18302
/cc @timo @denittis @jpwhiting
Edited by Simon McVittie