use actual DDS API types when possible

[adamsj-ros]

I don't think there's anything technically wrong here, but I think this is harder to read/maintain/verify than it should be. In OpenDDS/rosidl_typesupport_opendds#18 some types were changed from void* to their actual DDS API types, but these were not. I think we should do a follow-on PR in that repo to make this more consistent.

Originally posted by @mitza-oci in https://github.com/oci-labs/rmw_opendds/diffs/4