[EVP] Introduce "nonce" to test::GetFormData and use it in tests

In this CL, we allow callers of test::GetFormData to also set "nonce"
in fields.

With that, we can now use it in tests that require setting "nonce",
which is also added to this CL.

Bug: 380367784
Change-Id: I309029b84ced564f30962dfb7de04d356cc9c6fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6973355
Commit-Queue: Sam Goto <goto@chromium.org>
Reviewed-by: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1520961}