Make CoreSDKError Equatable

[KunJeongPark]

Summary of changes

• Make CoreSDKError Equatable and make static constants in CardError and PayPalError public so merchants can do this:

if let error {
  if error == CardError.threeDSecureCanceledError {
      // handle cancel case
   } else {
    // handle other errors 
 }

Checklist

• Added a changelog entry

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @KunJeongPark

[KunJeongPark]

I will also make other Error enums (eg. NetworkClientErrors) and static constants public.

I haven't seen a case where merchant needs to act on any error other than cancellation, but I think it's consistent to make all error types public.

[sshropshire]

q: is it possible to make vaultError a CoreSDKError? to prevent needing a cast here?

[KunJeongPark]

yes, good call. Actually, clientID fetching can also throw an error in the vault function above, so that's why I cast it here.

[sshropshire]

This is awesome! 🔥