Port to Qt 6

"src/libs/extensionsystem/optionsparser.cpp:122:24: error: call of overloaded ‘transform<template<class _Tp, class _Alloc> 
    class std::vector>(const QVector<ExtensionSystem::PluginSpec*>, ExtensionSystem::Internal::OptionsParser::checkForTestOptions()::<lambda(ExtensionSystem::PluginSpec*)>)’ is ambiguous

stringtable.cpp:127:65: error: cannot convert ‘QString::DataPointer’ {aka ‘QArrayDataPointer<char16_t>’} to ‘QArrayData*’ in initialization
stringtable.cpp:128:22: error: invalid use of member function ‘bool QArrayData::ref()’ (did you forget the ‘()’ ?)
stringtable.cpp:128:26: error: expected ‘;’ before ‘isShared’ 
stringtable.cpp:128:26: error: ‘isShared’ was not declared in this scope
stringtable.cpp:128:50: error: invalid use of member function ‘bool QArrayData::ref()’ (did you forget the ‘()’ ?)

C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.25.28610\include\xutility(1492): error C2672: 'operator __surrogate_func': no matching overloaded function found
C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.25.28610\include\list(1678): note: see reference to function template instantiation 'void std::_Debug_order_unchecked<std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<_Ty>>>,std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<_Ty>>>,_Pr2&>(_InIt,_Sentinel,_Pr)' being compiled
        with
        [
            _Ty=ProValueMap,
            _Pr2=std::less<void>,
            _InIt=std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<ProValueMap>>>,
            _Sentinel=std::_List_unchecked_iterator<std::_List_val<std::_List_simple_types<ProValueMap>>>,
            _Pr=std::less<void> &
        ]
C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.25.28610\include\list(1661): note: see reference to function template instantiation 'void std::list<ProValueMap,std::allocator<ProValueMap>>::_Merge1<std::less<void>>(std::list<ProValueMap,std::allocator<ProValueMap>> &,_Pr2)' being compiled
        with
        [
            _Pr2=std::less<void>
        ]