Since 6.10, QDoc is capable of generating links to the declaration in
the source code for each documented C++ API entity in their `Detailed
description`.
Add the required configuration to enable this feature in online
documentation builds.
Change-Id: Iaafabc5aea50a6cd72549bb1c04007bb4de498ca
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
cc07564978