[CredManUi] Honor preferDefaultProvider for the create flow

When the app specifies a preferDefaultProvider in their create-cred
request, and the app has the CREDENTIAL_MANAGER_SET_ALLOWED_PROVIDERS
permission, then that preferred provider will take precedent over the
user specified preferred provider, only during the lifetime of this
single request.

Bug: 276777936
Test: manual (see bug for videos)
Change-Id: I70a130f4cbe3a32ce38b7b6e2925e7e52e46b727