docs/qapidoc: Add "the members of" pointers

docs/qapidoc: Add "the members of" pointers

Add "the members of ..." pointers to Members and Arguments lists where
appropriate, with clickable cross-references - so it's a slight
improvement over the old system :)

This patch is meant to be a temporary solution until we can review and
merge the inliner.

The implementation of this patch is a little bit of a hack: Sphinx is
not designed to allow you to mix fields of different "type"; i.e. mixing
member descriptions and free-form text under the same heading. To
accomplish this with a minimum of hackery, we technically document a
"dummy field" and then just strip off the documentation for that dummy
field in a post-processing step. We use the "q_dummy" variable for this
purpose, then strip it back out before final processing. If this
processing step should fail, you'll see warnings for a bad
cross-reference. (So if you don't see any, it must be working!)

Signed-off-by: John Snow <jsnow@redhat.com>
Message-ID: <20250311034303.75779-58-jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>