qmltyperegistrar generates anonymous base types only for direct ancestor

We've added code to auto-generate descriptions of base classes to qmltyperegistrar when encountering a type whose base class is not yet registered. This works but is rather limited. The base classes are only generated recursively if they contain QML_ELEMENT or similar macros. Otherwise only the first base class is registered. Therefore, if you have a hierarchy MyType -> QAbstractListModel -> QAbstractItemModel -> QObject, for example, only MyType and QAbstractListModel are made available to QML tooling automatically. You can easily work around this by either creating your own anonymous types or depending on modules that provide the necessary types, but as we are making an effort we should do so properly.

Furthermore, properties, signals and methods are also not examined for types not tagged with QML_ELEMENT or similar.