qt/qml: bulk refactor

This set of patches tries to optimize performance by leveraging Qt specific things.

All the changes are made automatically by a text editor. It is marked as Draft because it requires extensive testing and opinions.

I have not spotted any property which is overridden, so every property is marked as FINAL. However, this must be checked.

Quote from Qt docs:

The presence of the FINAL attribute indicates that the property will not be overridden by a derived class. This can be used for performance optimizations in some cases, but is not enforced by moc. Care must be taken never to override a FINAL property.