qapi: Introduce QAPI_LIST_APPEND

qapi: Introduce QAPI_LIST_APPEND

Similar to the existing QAPI_LIST_PREPEND, but designed for use where
we want to preserve insertion order.  Callers will be added in
upcoming patches.  Note the difference in signature: PREPEND takes
List*, APPEND takes List**.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210113221013.390592-4-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>