qemu-config: parse configuration files to a QDict

qemu-config: parse configuration files to a QDict

Change the parser to put the values into a QDict and pass them
to a callback.  qemu_config_parse's QemuOpts creation is
itself turned into a callback function.

This is useful for -readconfig to support keyval-based options;
getting a QDict from the parser removes a roundtrip from
QDict to QemuOpts and then back to QDict.

Unfortunately there is a disadvantage in that semantic errors will
point to the last line of the group, because the entries of the QDict
do not have a location attached.

Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210524105752.3318299-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>