* Drop deprecation warnings for now-dropped items
* Use the 'qt6' define and a new \nothing doc macro to conditionally
document items on Qt 6
* Add a custom module header for docs that pulls in also Vulkan headers
* Add \internal command for internal classes/functions
* Move QtGUI-related code snippets from widgets to gui docs
Change-Id: Ieb386b96631a49568d09059906d307c45c01d93a
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
239982901b