key path conversion

<%_
import SourceryRuntime

let ConvertibleTypes = types.implementing["KeyPathConvertible"]
-%>

<%_ for Convertible in types.implementing["KeyPathConvertible"] { -%>
extension PartialKeyPath where Root == <%= Convertible.name %> {
    var stringValue: String {
        switch self {
        <%_ for member in Convertible.variables { -%>
        case \<%= Convertible.name %>.<%= member.name %>: return "<%= member.name %>"
        <%_ } -%>
        default: fatalError("Unexpected key path")
        }
    }
}

<%_ } -%>