make enum class SegmentType a ": short"
convert enum Hidden into global enum class

after having seen how it is done in e1b1246
convert enum AlignmentFlag into enum class
small step further in converting enum Repeat into enum class

not there yet, as at least overloaded operators for |, &, |=, &= and ~ would be needed to make this fully working. And even then it'd require lots of explict casting. This is most probably not be worth the price...
convert enum ElementFlag into enum class
convert enum LayoutFlag into enum class
convert enum ArticulationShowIn into enum class
convert unnamed enum into enum Col

making it a class, just to cast back to int, is not worth the effort
convert unnamed enum into enum class State
convert unnamed enum into enum AmbitusControl

making it a class, just to cast back to int, is not worth the effort
convert unnamed enum into enum ImageControl

making it a class, just to cast back to int, is not worth the effort
convert unnamed enum into enum class Icons
convert enum GuitarProError into enum class
convert enum PaletteCommand into enum class
convert unnamed enum into enum class SeqMsgId
convert unnamed enum into global enum class Transport
formatting fixes
rebase to fix conflict with f87cb01
fix #29810: workaround for Mac/Xcode bug
addressing @lasconic's concerns