docs for property accessors don't inherit \preliminary from the property docs

This came up while trying to make clear that most of the API (both QML and C++ ) of https://doc.qt.io/qt-6/qml-qtquick-textdocument.html and https://doc.qt.io/qt-6/qquicktextdocument.html is in Tech Preview. There is a blanket \note at the top, but someone might miss it. (I have been working on https://codereview.qt-project.org/c/qt/qtdeclarative/+/545664 ) So this is not quite clear: if a property has \preliminary and then C++ accessor docs end up being generated, are we sure that the accessors are also shown to be \preliminary or tech preview? They should be, IMO, and I should not have to repeat myself by adding accessor docs just for the purpose of adding \preliminary to them.

Maybe the property change notifier signals should be assumed \preliminary too, unless otherwise documented? I'm not sure.