Qt Writing Guidelines: Update QDoc's Qt C++ and QML style guidelines

The Qt Writing Guidelines needs an updated Qt C++ and QML style guidelines. The intent of these guidelines are to inform the Qt community how QDoc is to be used for documenting C++ and QML.

-copy Qt Project related content from the QDoc Manual/Guide to the wiki, where the audience is for the Qt project users.

-make the QDoc manual more neutral. QDoc manual is for any QDoc user, not just Qt Project.

-work with safiyyah to prepare and edit the QDoc manual for the move.

Reference:

-QDoc Manual's guide content https://doc.qt.io/qt-6/qdoc-guide.html

-Qt Writing Guidelines: https://wiki.qt.io/Qt_Writing_Guidelines