[FCLite] Make FC Lite available in MPE

[mats-stripe]

Summary

This integrates FC Lite into MPE. The main idea here is we first check if the full SDK is available, use that if so, and otherwise fallback on FC Lite.

Important

This PR does not release FC Lite. There is a guardrail in place (fcLiteFeatureEnabled) that prevents it from being accessed, and this is only currently enabled by our example apps.

Motivation

Testing

Manual testing done! Here's the Payment Sheet example app:

Screen.Recording.2025-03-27.at.1.12.51.PM.mov

And the Financial Connections example app:

Screen.Recording.2025-03-27.at.1.15.08.PM.mov

Changelog

N/a

[mats-stripe]

Drive-by fix. Our linter was yelling about this line

[github-actions]

⚠️ Public API changes detected:

StripePaymentSheet

- public var link: StripePaymentSheet.PaymentSheet.LinkConfiguration
- public struct LinkConfiguration {
- public var display: StripePaymentSheet.PaymentSheet.LinkConfiguration.Display
- public enum Display : Swift.String {
- case automatic
- case never
- public init?(rawValue: Swift.String)
- public typealias RawValue = Swift.String
- public var rawValue: Swift.String {
- get
- }
- }
- public init(display: StripePaymentSheet.PaymentSheet.LinkConfiguration.Display = .automatic)
- }

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.