Create a tool to help users migrate from Qt5 to Qt6

Users/companies need good tooling to support migrating from Qt5 to Qt6. Among several options, clazy probably provides the best UX and we should study and implement the required clazy configs to analyse the code and suggest changes, required by Qt6. Python scripts have been considered as an alternative option, but instead of string replacements, clazy would provide nicer suggestions. 

Basic fixes

Signature fixes

Header Fixes

Deprecated QDir API

Deprecated QTextStream modifiers in global namespace

Replace use of QTextStream modifiers in global namespace by their Qt:: variants, e.g.

out << hex << i; 

to

out << Qt::hex << i; 

(if Qt namespace is not included)

API:
QTextStream &bin(QTextStream &s);
QTextStream &oct(QTextStream &s);
QTextStream &dec(QTextStream &s);
QTextStream &hex(QTextStream &s);
QTextStream &showbase(QTextStream &s);
QTextStream &forcesign(QTextStream &s);
QTextStream &forcepoint(QTextStream &s);
QTextStream &noshowbase(QTextStream &s);
QTextStream &noforcesign(QTextStream &s);
QTextStream &noforcepoint(QTextStream &s);
QTextStream &uppercasebase(QTextStream &s);
QTextStream &uppercasedigits(QTextStream &s);
QTextStream &lowercasebase(QTextStream &s);
QTextStream &lowercasedigits(QTextStream &s);
QTextStream &fixed(QTextStream &s);
QTextStream &scientific(QTextStream &s);
QTextStream &left(QTextStream &s);
QTextStream &right(QTextStream &s);
QTextStream &center(QTextStream &s);
QTextStream &endl(QTextStream &s);
QTextStream &flush(QTextStream &s);
QTextStream &reset(QTextStream &s);
QTextStream &bom(QTextStream &s);
QTextStream &ws(QTextStream &s);

Removed QMap::insertMulti()

replace

QMap<QString, QString> m;
m.insertMulti("foo", "bar")

with

QMultiMap<QString, QString> m;
m.insertfoo", "bar")

Changed semantics of QProcess::start("foo bar")

replace

QProcess p;
p.start(stringContainingACommandWithArguments);

with

QProcess p;
p.startCommand(stringContainingACommandWithArguments);

forward declarations of QStringList (and possibly others)

remove

class QStringList;

and add the include directive

#include <QtCore/qcontainerfwd.h>

Further candidates

This is a rabbit hole. The APIs are quite different. Porting hints can be found in QRegularExpression's documentation.

Other:

• Add a fixit to missing-qobject-macro