Migrate to Qt 6

[Integral-Tech]

Qt 6 has been released for several years.
It would be greater if SASM could be migrated to Qt6.

[a17r]

At this point in time, Linux distributions are starting to track which packages are blocking a future Qt5 cleanup. Real Qt Company OSS support stopped back in 2020, when public availability of LTS releases started to be delayed for 1 year, stable branch repository access got closed down (with 5.15 branch repository receiving any new LTS tag one year after commercial release) and only Qt6-relevant bugs are being fixed (then backported) since then.

At least Gentoo and Ubuntu are entertaining Qt5 porting trackers by now, for Gentoo, Qt5 revdep cleanups are in full swing already.
https://bugs.gentoo.org/show_bug.cgi?id=qt5-removal
https://ubuntu-archive-team.ubuntu.com/transitions/html/qt5-removal.html

The good news is that the porting effort to Qt6 is supposed to be much smaller than from Qt4 to Qt5. Links:
https://doc.qt.io/qt-6/portingguide.html
https://www.qt.io/blog/references-and-hints-about-porting-from-qt5-to-qt6
https://www.qt.io/blog/porting-from-qt-5-to-qt-6-using-qt5compat-library

[noynaert]

I am currently getting the following message:

Info: runtime org.kde.Sdk branch 5.15-23.08 is end-of-life, with reason:
We strongly recommend moving to the latest Qt 5.15-based stable version of the Platform and SDK
Info: applications using this runtime:
io.github.dman95.SASM