Make AppSettingsHelperProtocol STP

[porter-stripe]

Summary

• An accidentally public protocol, made it STP

Motivation

https://docs.google.com/document/d/1DVnqjz5gLAP_JbjxZJ0Ptdv72hO0jTfreYx6_CdcGn0/edit?tab=t.0

Testing

• Compiler

Changelog

N/A (should have never been public, no mention in change log, probably no one using it)

[github-actions]

⚠️ Public API changes detected:

StripeCameraCore

- var canOpenAppSettings: Swift.Bool { get }
- func openAppSettings()

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.