Explicitly document behavior for QFileInfo if file is directory

Despite the name, QFileInfo can also represent a directory. The behavior of methods like QFileInfo::path() can then be confusing, see e.g. https://forum.qt.io/topic/153585/correctly-create-qdir-from-qfileinfo/10

Suggestion: Make the distinction between (file) object and file in the documentation. This is done already partially. COmpare e.g.

> Returns the path of the object's parent directory as a QDir object.

vs

> Returns the file's path.

Also, make behavior of https://doc.qt.io/qt-6/qfileinfo.html#absoluteDir more explicit, e.g. with a code snippet.