* Qt 6.8.1
Bumps minimum glibc to 2.35, and minimum macOS to 12
* Drop generation of Qt5 packaged build
Closes#3615
* Include qt6 requirements in aqt wheel; drop extra deps
* Fix aqt wheels growing over time
- Windows was on 6.4 as some users reported slowdowns; we'll need to
confirm whether they have come back in the next build.
- Linux has been held back due to https://bugreports.qt.io/browse/QTBUG-114635
