Port API documentation to qdoc

See https://mail.kde.org/pipermail/kde-devel/2024-July/002849.html

TL;DR Our C++ API documentation has some issues, our QML API documentation has a lot of issues.

To fix those we are porting our API documentation from Doxygen to qdoc.

See https://invent.kde.org/teams/documentation/sprints/-/boards > QDoc Port for progress