[chromedriver] Virtual authenticator large blobs

This change implements the webauthn:extension:largeBlob extension
capability, adding large blob support for virtual authenticators.

The webauthn:extension:largeBlob capability:
 * Adds an option on authenticator creation to enable large blob
   support.
 * Allows setting and retrieving the large blob through AddCredentials
   and GetCredentials.

https://w3c.github.io/webauthn/#sctn-authenticator-extension-capabilities

This is part of the WebAuthn Testing API
https://docs.google.com/document/d/1bp2cMgjm2HSpvL9-WsJoIQMsBi1oKGQY6CvWD-9WmIQ

Bug: chromedriver:3631
Change-Id: Ie8be5a36f78068c1f7f168987e8aa531fef6077a
Cq-Include-Trybots: luci.chromium.try:linux-wpt-identity-fyi-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488183


Reviewed-by: Shengfa Lin <shengfa@google.com>
Commit-Queue: Shengfa Lin <shengfa@google.com>
Cr-Commit-Position: refs/heads/master@{#820058}