[FedCM] Integrate new_accounts_idp with Android UI

Currently on button mode when user signs in with a new account, they are
shown the account chooser and then the request permission dialog of
their newly signed-in account. Integrating with new_accounts_idp allows
the user to skip the redundant account chooser step.

Demo
https://issues.chromium.org/issues/353770052#comment3

Low-Coverage-Reason: TRIVIAL_CHANGE Simple data holder definition.
Bug: 353770052
Change-Id: I0aa021380cc62e8f9b7c97cb4c3c8d2636f18553
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5750543
Commit-Queue: Zachary Tan <tanzachary@chromium.org>
Reviewed-by: Nicolás Peña <npm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1336698}