Add some embedded namespaces

[porter-stripe]

Summary

• Adds some missing namespaces for embedded
• All backward compatible

Motivation

• Cleaner API

Testing

Compiler

Changelog

N/A

[github-actions]

⚠️ Public API changes detected:

StripePaymentSheet

- public var cardBrandAcceptance: StripePaymentSheet.PaymentSheet.CardBrandAcceptance
+ public var cardBrandAcceptance: StripePaymentSheet.EmbeddedPaymentElement.CardBrandAcceptance
+ public typealias BrandCategory = StripePaymentSheet.PaymentSheet.CardBrandAcceptance.BrandCategory
+ public typealias CardBrandAcceptance = StripePaymentSheet.PaymentSheet.CardBrandAcceptance

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 and bypass this check.

ℹ️ If this comment appears to be left in error, make sure your branch is up-to-date with master.

[joyceqin-stripe]

Is BrandCategory used anywhere?

[porter-stripe]

Yes, but not explicitly. It is used under the CardBrandAcceptance name-space. So, EmbeddedPaymentElement.Configuration.CardBrandAcceptance.BrandCategory. It's used in the card brand filtering API.