This property is similar to ``org.freedesktop.DBus.Interfaces`` property
on the bus interface: it's an array of strings listing the extra
interfaces and capabilities available, in a convenient way.

Most interfaces are implicit, as they are required. For
``org/qemu/Display1_$id``, we can list the Keyboard And Mouse
interfaces. Those could be optional.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230606115658.677673-9-marcandre.lureau@redhat.com>