Demo App changes for Vault App Switch

[KunJeongPark]

Reason for changes

• Allow app switch options in demo app with supporting data structures

Summary of changes

• App switch toggle
• Make views on vaulting take in UI selection options, avoid business logic
• app_switch_context created in experience_context if app switch selected.
• only send in app switch URL to AppSwithContext initializer

Checklist

• Added a changelog entry

Authors

List GitHub usernames for everyone who contributed to this pull request.

• @KunJeongPark

[KunJeongPark]

I am checking with checkout team on this, whether this can remain custom url scheme.
Ideally, we have ability to have happy path return_url back from PayPal app from the app switch context app_url.
I will make changes on it on subsequent PRs depending on answer we get.
For web checkout, iOS SDK constructs the ASWebAuthentication launch url with return_uri param that contains SDK specific custom url scheme, "sdk.ios.paypal"
So we can default to this in case of ineligibility or app not installed.

[sshropshire]

🌊