Qt6support

This is an initial attempt to make KStars support Qt6 while retaining support for QT5. It does build fine on my Mac, but there are some issues when running it, particularly related to INDI. I had to make a large number of changes to make this work, and some might not be the best solutions. I am most concerned about the changes related to KLocalizedString, midref, QStringRef, and some pointer changes. I am not concerned about changes to QtConcurrent and QRegularExpression since I already had to make those changes in StellarSolver.