fix: Support multi-argument version of unnest

[charithe]

Currently, sqlc errors out when it encounters the multi-argument version of the UNNEST function. This is because the function is not marked as variadic. Instead, the argument type is defined as anymultirange.

Fixes #3507

[charithe]

Not sure why the managed-db tests fail and how to go about debugging them 🤔

[StevenACoffman]

@kyleconroy Do you have a chance to review this PR? I believe this works well and would go nicely with some recent improvements.

[akalmyk]

Is there any change to review this PR please? It's been almost a year

[rustik666]

@kyleconroy just a kind reminder, it would be highly appreciated if you will find some time to review this PR. I just also have the same issue as folks have and it would be great to have it merged.

Thanks a lot in advance! 👍

[StevenACoffman]

@andrewmbenton PTAL