[digital credentials] Add an example of OpenID4VP over the DC API

Add an example in browser tests with a more realistic OpenID4VP
request that we can use as a contract with the underlying platform.

Bug: 1416939
Change-Id: If39b172a4519f85bbba5ac6e5d289eea148c4a44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5384902


Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Auto-Submit: Sam Goto <goto@chromium.org>
Commit-Queue: Sam Goto <goto@chromium.org>
Reviewed-by: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279142}