Fix PaymentCardTextField bugs

[rkrueger11]

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Fixes:

1. Unintentional autofocusing functionality on Android with the PaymentCardTextField component
2. Replaces currentlyFocusedField call (currentlyFocusedField is deprecated and will be removed in a future release. #680)

[pvinis]

Why were all these issues marked as wont-fix and closed? Is this lib not maintained anymore? @cybergrind

[aganov]

@pvinis #708 We have to wait for official RN library from Stripe. Meanwhile you can keep your own fork with critical patches applied.

[Sheharyar566]

Not sure about that but @cybergrind should at least accept PRs (while setting a disclaimer at Readme that the lib isn't maintained).... Disclaimer is one thing... but please at least accepts PRs, so that we have something to work with while the official library isn't released.