fix return struct as values

[lassade]

Generates extra metada to fix marlersoft/zigwin32#6

[marler8997]

Thanks for the contribution! Do you mind cleaning up the commit a bit? Removing the comments, the ".csproj.user" file and see if you can undo the line ending changes in the csproj file and squash into 1 commit? If not I'll probably do it myself and mark you as co-author.

[lassade]

now it's done