AppMan: Port from manual Q_CLASSINFO()+dumpqmltypes to QML_ELEMENT+qmltyperegistrar

The current implementation doesn't take advantage of the standard QML tools, which makes it error-prone (see QTBUG-114355 and QTBUG-114356 for example):

• The QML-facing C++ classes don't use QML_ELEMENT/QML_UNCREATABLE()/QML_SINGLETON, but rather Q_CLASSINFO("AM-QMLType", "QtApplicationManager.ModuleName/<TypeName> [maj.min] [UNCREATABLE][SINGLETON]")
  • Example: https://github.com/qt/qtapplicationmanager/blob/v6.5.1/src/main-lib/applicationinstaller.h#L31

• The custom Q_CLASSINFO information is parsed by a custom implementation of qmlplugindump/qmltyperegistrar for generating qmldir files.
  • This tool looks for staticMetaObjects of classes that are manually listed in a QVector: https://github.com/qt/qtapplicationmanager/blob/v6.5.1/src/tools/dumpqmltypes/dumpqmltypes.cpp#L46-L84

These should be ported to use standard QML integration techniques to simplify maintenance and avoid errors:

• Use QML_ELEMENT and friends
  • https://doc.qt.io/qt-6/qtqml-cppintegration-definetypes.html

• Use the CMake QML API
  • https://www.qt.io/blog/introduction-to-the-qml-cmake-api
  • https://doc.qt.io/qt-6/qt-add-qml-module.html