chore: keep pointer receiver consistent in generated go code

[jedevc]

Some linters don't like this, which is a small issue, but it's super easy to fix :D

[aweris]

🚀

[sipsma]

This change seems fine, but sort of confused that a linter would complain about this since it's completely legit+expected to sometimes need a mix of pointer and non-pointer receivers. Hopefully it's intelligent enough to identify those cases. Just mentioning since I don't think we can necessarily guarantee we will always follow this rule indefinitely.

[jedevc]

Woops, test failures are entirely legitimate here.

When implementing the MarshalJSON function, this was deliberate: we directly call json.Marshal on values being returned from user-defined functions - which can be objects directly, instead of pointers to those objects.

In actuality, it should be the other way round here! We should be doing the same for concrete iface definitions as well (since those can also be returned from functions, in which case the method wouldn't have been called).

[jedevc]

Ugh, can't re-open this PR since I force-pushed the branch after closing it? Opened #7219 instead.