convert: conversion strategies for struct unions

[kristoff-it]

At the moment, given the following files, conversion will succeed:

build.json

{
        "name": "zine",
        "version": "0.0.1"
        "dependencies": {
                "foo": {
                        "Remote": {
                                "url": "https",
                                "hash": "aaa"
                        }
                },
                "bar": {
                        "Local": {
                                "path": "/usr"
                        }
                }
        }
}

build.ziggy-schema

root = Project

struct Project {
    name: bytes,
    version: bytes,
    dependencies: map[Remote | Local],
}

struct Remote {
   url: bytes,
   hash: bytes,   
}

struct Local {
  path: bytes,
} 

Result:

{
    .name = "zine",
    .version = "0.0.1",
    .dependencies = {
        "foo": Remote {
            .url = "https",
            .hash = "aaa",
        },
        "bar": Local {
            .path = "/usr",
        },
    },
}

The goal is to also make the following JSON files succeed at importing:

Shape matching:

{
	"name": "zine",
	"version": "0.0.1"
	"dependencies": {
		"foo": {
			"url": "https",
			"hash": "aaa"
		},
		"bar": {
			"path": "/usr"
		}
	}
}

type field:

{
	"name": "zine",
	"version": "0.0.1"
	"dependencies": {
		"foo": {
			"type": "Remote",
			"url": "https",
			"hash": "aaa"
		},
		"bar": {
			"type": "Local",
			"path": "/usr"
		}
	}
}