Also register complex D-Bus types when running under qdbus

When running inside qdbus, we generate the meta objects a little
differently. Previously, for unknown types we'd simply have a -1 as the
type ID in the meta object, but this doesn't work in Qt 5 (has
apparently never worked). So simply register a type with the metatype
system and let QMetaObject do its thing.

[ChangeLog][qdbus]Fixed a bug that caused the qdbus tool to crash
when trying to display remote interfaces that had complex types
without a matching base Qt type.

Task-number: QTBUG-36524
Change-Id: Ifef65b340dc89d3295ed6ef00f2dcc60849ecb02
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>