[Feature] STPCardFormView should allow for customization similar to STPPaymentCardTextField.

[ryanluce]

Is your feature request related to a problem? Please describe.

STPCardFormView should allow for the textfields within it to be customized similar to STPPaymentCardTextField. We have specific fonts for our app, much like other apps. We can implement them in STPPaymentCardTextField but not STPCardFormView.

Describe the solution you'd like

STPCardFormView should implement a similar private allFields property and iterate through them with setters for font, font color etc.

Describe alternatives you've considered

An alternative would be to just make the textfields in STPCardFormView to be public so they're accessible and not internal when using the SDK through a dependency manager like cocoapods.

Additional context

Add any other context or screenshots about the feature request here.

[davidme-stripe]

Thanks for filing this! I think this is a duplicate of #1932, we'll track this request there.