Replicate the "main": false patch from Parcel

[benjervis]

Unfortunately, this ecosystem pollution has spread to our world as well, and we've inherited Parcel's problem of not parsing the main field as a boolean.

This PR just replicates Devon's patch into Atlaspack, including his test.

[yamadapc]

I think we should consider treating main specifically rather than adding catch-all ok_or_default to the fields.

With this change the following invalid package.json will get parsed:

    let pkg: PackageJson = serde_json::from_str(r#"{"name":1234}"#).unwrap();
    assert_eq!(pkg.name, "");

name will be set to "" which is not a really semantically valid value, a similar problem will happen for the other fields.