Use manifold's optional parameters to make records nicely copyable

[rsmckinney]

Provide a feature, perhaps within manifold-params, to make records copyable using optional/named parameters.

public record Book( 
        String title,
        String author,
        Kind kind = Nonfiction,
        Language language = English,
        Integer edition = null) {

    // generated
    public Book copy(
            String title = this.title,
            String author = this.author,
            Kind kind = this.kind,
            Language language = this.language,
            Integer edition = this.edition) {    
        return new Book(title, author, kind, language, edition);
    }
}  

Book book = new Book("Florida Gardening", "David The Good", edition: 2);
Book rubook = book.copy(language: Russian);

Note, this feature depends on #697

[rsmckinney]

Experimental copyWith(...) method generated for records when manifold-params is in use. This is likely a temporary implementation until optional parameters work with extension methods, and extension methods work with source, as opposed to compiled classes.