closes #45851

The PR ...

• adds a public client test-app-pub to testrealm.json
• adds a comprehensive test using the new OAuthClient APIs (i.e. OID4VCPublicClientTest)
• adds support for error page/redirect to the AuthorizationRequest
• removes dependency on OID4VCIssuerEndpointTest.getCredentialOfferUriUrl()

while working on this, I discovered these follow up issues ...

• Pre-Auth TokenRequest does not natively support OID4VCAuthorizationDetail
• Pre-Auth AccessToken does not have expected scopes [openid, oid4vc_natural_person_jwt] (still works)
• Issuer AccessToken does not contain credential-offer-create role (still works)
• OAuthClient.doLogin cannot handle error page/redirect

Depends on #46356