Pref multi sampling enum

[ronso0]

based on #12794

Currently this is a mess.
Got it working to a state where it builds but the linker complains, but I'm not motivated to continue this polishing atm.

[ 98%] Linking CXX executable mixxx
mold: error: undefined symbol: mixxx::staticMetaObject
>>> referenced by dlgprefinterface.cpp
>>>               libmixxx-lib.a(dlgprefinterface.cpp.o):(QtPrivate::MetaObjectForType<mixxx::MultiSamplingMode, void>::metaObjectFunction(QtPrivate::QMetaTypeInterface const*))>>> referenced by dlgprefinterface.cpp
>>>               libmixxx-lib.a(dlgprefinterface.cpp.o):(QtPrivate::QDebugStreamOperatorForType<mixxx::MultiSamplingMode, true>::debugStream(QtPrivate::QMetaTypeInterface const*, QDebug&, void const*))>>> referenced by dlgprefinterface.cpp
>>>               libmixxx-lib.a(dlgprefinterface.cpp.o):(QtPrivate::QMetaTypeForType<mixxx::MultiSamplingMode>::getLegacyRegister()::{lambda()#1}::_FUN())