Fix multiple incorrect \l (link) command arguments that were not
captured by documentation testing in CI.
Add missing \endqml and \endcode commands to code snippets.
Convert \sa commands that are meant to be related to specific \section
commands into manual 'See also' paragraphs. Otherwise, they are listed
at the bottom of the page.
Pick-to: 6.7
Change-Id: Icf2a97f63b8b8cdec2d9398448d28759dabdb06b
Reviewed-by: Andreas Eliasson <andreas.eliasson@qt.io>