Fix issue of removed PM sticking around

[tillh-stripe]

Summary

This pull request fixes an issue in FlowController where an outdated payment method would stick around and would potentially be used for payment confirmation.

The issue occurred when removing the currently selected payment method and then closing PaymentSheet without explicitly selecting a new one. We’re addressing this issue by including the current payment method selection in PaymentOptionResult.Canceled and updating FlowControllerViewModel.paymentSelection.

Motivation

Resolves #6385

Testing

• Added tests
• Modified tests
• Manually verified

Screenshots

Before	After
before screenshot	after screenshot

Changelog

[FIXED] Fixed an issue where FlowController.getPaymentOption() and PaymentOptionCallback might return an outdated payment option in some cases.

[tillh-stripe]

I’ve been having issues getting this tested in PaymentOptionsViewModelTest, as I couldn’t get the PaymentOptionsStateMapper to emit a new state even when one of its inputs changed. I plan on getting rid of some of the PaymentOptionsState logic though (with this), so any test I’d write would become obsolete anyway. If anyone is feeling strongly about adding a test, I can continue to try, but I lean towards merging in the current state.

[tillh-stripe]

Added a note to the changelog.