Skip default scalars

[jvliwanag]

Currently, default scalars are hardcoded on the generated code -- Int, Float, String, Boolean, and ID. Requesting a feature to skip defining this scalars.

My particular use case is I wish to override ID, since the ID I'm receiving follows a certain format which would be better off represented as a custom struct with its own serde serializer, deserializer.

Perhaps introducing a skip_default_scalars option makes sense.

[bbigras]

Any progress on this?