[Feature] make 'setPostalCode' on 'CardInputWidget' public

[john-mejia]

Is your feature request related to a problem? Please describe. We use the setter methods on CardInputWidget for testing purposes. After requiring a postal code in our application we can no longer write a test to confirm a car is valid. A potential solution is reaching into the view hierarchy and manipulating the TextInputLayout directly but it feels odd that this is the only API that is not exposed.

Describe the solution you'd like Expose setPostalCode similarly to setCardNumber, setCvcCode, setExpiryDate, and setCardNumber

Describe alternatives you've considered Reaching into the view hierarchy and manipulating the TextInputLayout directly but it feels odd that this is the only API that is not exposed.

Additional context We programmatically set each field and test card validity on each step of user input.