Add missing FPX bank support

[ryanjeffares-stripe]

Summary

Added support for FPX bank options that are available in Stripe.js but have been missing from the iOS SDK: Agrobank, Bank of China, Deutsche Bank, Public Bank Enterprise, MBSB Bank, BNP Paribas, and Citibank. Refactored some of the code to use map lookups instead of long switch statements. Displaying banks in ascending alphabetical order as is required by the financial partner.

Motivation

New FPX bank support was added to the API here and is available in Stripe.js, bringing this SDK to parity.

Testing

Changelog

[github-actions]

⚠️ Public API changes detected:

StripePayments

Public API

+  case agrobank
+  case bankOfChina
+  case bnp_paribas
+  case citibank
+  case deutscheBank
+  case mbsb_bank
+  case publicBankEnterprise

If you are adding a new public API consider the following:

• Do these APIs need to be public or can they be protected with @_spi(STP)?
• If these APIs need to be public, assess whether they require an API review.

If you are modifying or removing a public API:

• Does this require a breaking version change?
• Do these changes require API review?

If you confirm these APIs need to be added/updated and have undergone necessary review, add the label modifies public API to this PR to acknowledge the interface change.
Additionally, if you modified or removed an existing API, ensure you update the changelog to reflect the necessary version bump for your changes. Regular public API changes require a MAJOR version bump, and SPI API changes (other than declarations using only @_spi(STP) and/or @_spi(ReactNativeSDK)) require a MINOR or MAJOR version bump.

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