[Development] Qt 6 and C++17, slicing and dicing a master plan for it

[Ville Voutilainen]

I and Kari Oikarinen created an epic, some user stories, and further 
some sub-tasks what needs to be done related to C++17 usage in Qt 6.
The link to the epic, under from which you can navigate to the more 
detailed levels, is here:

https://bugreports.qt.io/browse/QTBUG-77477

Feedback, comments, suggestions etc. are welcome. We will most probably 
need to add much more 'meat' to the library-facility parts.