chore: allow mixing meta while merging Body.Data

[nekrich]

Ignore irrelevant generic types when merging Document.Body.Data.

I have a paginated request, and the response data has no meta and links because it’s irrelevant in the case when Meta is NoMetadata.

Also, made it possible to merge data with different API descriptions and errors.

[mattpolzin]

This looks like a nice improvement.

[mattpolzin]

Hmm, so I see the logic behind not caring about the OtherDescription or OtherError when merging the Document.Body because those are not stored in the Body. On the other hand, your changes to the merging implementation where MetaType == NoMetadata and LinksType == NoLinks seem less intuitive to me; they merge in a document body that does have metadata and/or links by throwing away the metadata and links from the body being merged in. I think the more intuitive result would be to keep the metadata and links from the document being merged in.

[mattpolzin]

I think I've maintained the spirit of this PR with my last change so I am going to merge this as it's sat open for far longer than I intended it to. Please let me know if I've mucked things up for you by changing the resulting type for the document merge.