Add root error info to public error

[tonidero]

Description

This is a possible approach to add root error info to public errors exposed by the SDK. Many times, we have nested errors, which makes discoverability of the root error difficult. This also hides actual StoreKit errors from being easily accessible, which some devs have asked about.

This PR adds a new property to the userInfo of the public error exposed by the SDK including relevant information about the root error. If the root error is a type of StoreKitError, we add some additional information related to that.

For example, when simulating an error getting products during the getOfferings call using StoreKit, a new property in userInfo rc_root_error will be added with the following structure:

{
    code = 4;
    domain = "StoreKit.StoreKitError";
    localizedDescription = "Item Unavailable";
    storeKitError =     {
        description = "not_available_in_storefront";
    };
}

or

{
    code = 2;
    domain = "StoreKit.Product.PurchaseError";
    localizedDescription = "Unable to Complete Purchase";
    storeKitError =     {
        description = "purchase_not_allowed";
    };
}

[tonidero]

I want to test this more and add some tests next week, but I wanted to get some feedback, specially from iOS folks, to make sure this makes sense and if there are other ideas to expose the root StoreKit error if any to developers 🙏

[tonidero]

My main concern with this approach is whether we only expose PublicError everywhere and/or if we use this method somewhere else... Need to research it a bit more.

[facumenzella]

I am afraid we might lose some keys because of an unwanted overlap. I would just add a prefix like rc_ to any new key we add to:

• be explicit on what we're adding
• avoid dropping useful data.

[tonidero]

Right, I added everything within a rc_root_error which I felt was enough as a namespace... I don't think it's worth adding to all nested properties then? Lmk if you think otherwise though!

[facumenzella]

nit: maybe we can add an explicit missing_value, otherwise people will think we missed it

[facumenzella]

I guess it would be useful to log what other error type we might be missing? 🤔

[tonidero]

Right, in this case I'm assuming it's because the root error is not a store kit error (which may happen in several situations). I could add a log here, but I think the situation may happen relatively often... Note that this method is only to add extra data to the userInfo map in case it's actually a StoreKit error.

[facumenzella]

I know it's a draft, but it would be great to list the keys we'll include in userInfo so people can just read it from here without going through the code

[tonidero]

Hmm so I included it in the docs for the asPublicError, but that's actually internal... I'm trying to figure out a better way to explain this, but maybe this is something we should add to the docs, for people that care to get the root error.