Graphile Export: detect hasOwn keys set on functions that aren't exportable
e.g. we had:

https://github.com/graphile/crystal/blob/c106e448228e792ae18b51348a4c2a191794a022/graphile-build/graphile-build/src/plugins/NodeIdCodecBase64JSONPlugin.ts#L2-L9

but the `isSyncAndSafe` property was not exported, so the plans ran differently in the source versus the exported schema.

Also, the name was exported as `encode` rather than `base64JSONEncode` so we should look into that too.

Have worked around this by making the function explicitly EXPORTABLE for now.