Add a copyWith method to the Product object

[g123k]

Hi everyone,

The Product object has non-final fields, but when we want to use the Product class as immutable, each client must code it. It would be nice to integrate it directly into the SDK.

[teolemon]

We should both be in bed ATM :-)

[monsieurtanuki]

We should both be in bed ATM :-)

[monsieurtanuki]

@g123k Currently in Smoothie we do copy Product data, in UpToDateProductProvider:

  // TODO(monsieurtanuki): move code to off-dart Product?
  Product copy(final Product source) => Product.fromJson(
        jsonDecode(jsonEncode(source.toJson())) as Map<String, dynamic>,
      );

Moving this copy code from Smoothie to off-dart would be much less painful than implementing copyWith, and would provide the same feature as all fields are not final and nullable.

[g123k]

I didn't know about this in the app 👍
The only here would be to create a "real" copyWith, not something based on a json, that requires calls to jsonDecode/jsonEncode