chore(generator): Fix deprecated QFlags default constructor warning

[jcfr]

This changes the initialization of m_type_flags to use TypeFlag::NoTypeFlags instead of 0. This resolves a deprecation warning related to the QFlags default constructor in Qt 5.15.2.

The warning fixed is:

/path/to/PythonQt/generator/typesystem.h:812:11: warning: ‘constexpr QFlags<T>::QFlags(QFlags<T>::Zero) [with Enum = ComplexTypeEntry::TypeFlag; QFlags<T>::Zero = int QFlags<ComplexTypeEntry::TypeFlag>::Private::*]’ is deprecated: Use default constructor instead [-Wdeprecated-declarations]
  812 |           m_type_flags(0)
      |           ^~~~~~~~~~~~~~~
In file included from /path/to/Qt/5.15.2/gcc_64/include/QtCore/qglobal.h:1304,
                 from /path/to/Qt/5.15.2/gcc_64/include/QtCore/qalgorithms.h:43,
                 from /path/to/Qt/5.15.2/gcc_64/include/QtCore/qlist.h:43,
                 from /path/to/Qt/5.15.2/gcc_64/include/QtCore/QList:1,
                 from /path/to/PythonQt/generator/parser/codemodel_fwd.h:46,
                 from /path/to/PythonQt/generator/parser/codemodel.h:46,
                 from /path/to/PythonQt/generator/abstractmetabuilder.h:45,
                 from /path/to/PythonQt/generator/abstractmetabuilder.cpp:42:
/path/to/Qt/5.15.2/gcc_64/include/QtCore/qflags.h:123:80: note: declared here
  123 |     QT_DEPRECATED_X("Use default constructor instead") Q_DECL_CONSTEXPR inline QFlags(Zero) noexcept : i(0) {}
      |                                                                                ^~~~~~