[KA] Add render tests for keyboard accessory buttons.

This CL renders the "Generate password" button and the "Dismiss"
button from the keyboard accessory.

Bug: 385172647
Change-Id: I55a6724163b85e3aaa61fc6210ef28e6cae5c4e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6994764
Reviewed-by: Piotr Kotynia <piotrkotynia@google.com>
Commit-Queue: Timofey Chudakov <tchudakov@google.com>
Cr-Commit-Position: refs/heads/main@{#1522744}