device/fido: add PIN support to |VirtualCtap2Device|

This will be needed for testing PIN support.

Change-Id: I274226528fe5fd3616d4e81233516e08f66406d9
Reviewed-on: https://chromium-review.googlesource.com/c/1484080
Commit-Queue: Adam Langley <agl@chromium.org>
Auto-Submit: Adam Langley <agl@chromium.org>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#636113}
9 files changed