Unify format for wit-workspace.json, wit-lock.json, wit-manifest.json

[mmjconolly]

wit-manifest.json and wit-workspace.json has

[
    {
        "commit": "abc",
        "name": "project",
        "source": "git@gh.com:acme/project"
    }
]

but wit-lock.json has

{
    "project": {
        "commit": "abc",
        "name": "project",
        "source": "git@gh.com:acme/project"
    }
}

and it seems to throw away the "project": dict key when parsing it anyway

Unify the file formats as the differences appear to not to be useful