[Test Automation] Kombucha: enable widget activation and accelerators

Adds ActivateSurface() and SendAccelerator() verbs.

Change-Id: Iedd5fd437d0bbd77d68f168dd848e9e823bf2037
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4049634


Commit-Queue: Dana Fried <dfried@chromium.org>
Reviewed-by: Kuan Huang <kuanhuang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1076495}