Pass link_mode to LAS creation

[tillh-stripe]

Summary

This pull request adds a link_mode field to the LAS creation request. If Link is not enabled, we send LINK_DISABLED just like Web does.

(cc @selinafeng-stripe)

Motivation

BANKCON-15655

Testing

Changelog

[mats-stripe]

LGTM, just one non-blocking suggestion

[github-actions]

⚠️ Public API changes detected:

StripePaymentSheet

- public var paymentMethodLayout: StripePaymentSheet.PaymentSheet.PaymentMethodLayout
- public enum PaymentMethodLayout {
- case horizontal
- case vertical
- case automatic
- public static func == (a: StripePaymentSheet.PaymentSheet.PaymentMethodLayout, b: StripePaymentSheet.PaymentSheet.PaymentMethodLayout) -> Swift.Bool
- public func hash(into hasher: inout Swift.Hasher)
- public var hashValue: Swift.Int {
- get
- }
- }

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• Do these APIs need to be public or can they be protected with @_spi(STP)?
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If you are modifying or removing a public API:

• Does this require a breaking version change?
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ℹ️ If this comment appears to be left in error, make sure your branch is up-to-date with master.

[github-actions]

🚨 New dead code detected in this PR:

OpenAuthenticatedWebViewMessageHandler.swift:11 warning: Class 'OpenAuthenticatedWebViewMessageHandler' is unused
ReturnedFromAuthenticatedWebViewSender.swift:11 warning: Struct 'ReturnedFromAuthenticatedWebViewSender' is unused

Please remove the dead code before merging.

If this is intentional, you can bypass this check by adding the label skip dead code check to this PR.

ℹ️ If this comment appears to be left in error, double check that the flagged code is actually used and/or make sure your branch is up-to-date with master.