qemu: Check ACLs before parsing the whole domain XML

qemu: Check ACLs before parsing the whole domain XML

Utilise the new virDomainDefIDsParseString() for that.

This is one of the more complex ones since there is also a function that
reads relevant metadata from a save image XML.  In order _not_ to extract
the parsing out of the function (and make the function basically trivial
and all callers more complex) add a callback to the function which will
be used to check the ACLs.

Fixes: CVE-2025-12748
Reported-by: Святослав Терешин <s.tereshin@fobos-nt.ru>
Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>