@api_default macro removes line info

```
julia> m = @which GitHub.pull_request(Repo("JuliaLang/julia"), 33779)
pull_request(repo, pr) in GitHub
```

In general, the '@api_default` is pretty annoying. It needs to be put on all methods and I don't see how it is better than just using a global or a keyword arg with a default value or something more normal.

Start by locating the @api_default macro and reproducing the @which GitHub.pull_request(...) example shown in the issue. Trace how the macro affects source locations; done means the example preserves useful line information and the macro's behavior is covered by a clear resolution.

Written by the indexing model from the issue text.