Doc: Fix fn commands for QSpan

Added a return type where it was missing as Clang would otherwise fail
to parse the command.

Qualified certain non-type template parameter that were based on a using
declaration inside the QSpan class.
An `\fn` command is parsed as a fake out-of-line definition. In that
context, the unqualified name will not be able to be solved by Clang,
resulting in an inability to match the element.

Pick-to: 6.7
Change-Id: I929ab5e8df4f7a6ef5d913266b584cd0393074e3
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>

0 files changed, 0 insertions, 0 deletions