[omnibox] Create OmniboxAnswerAction class

OmniboxAnswerAction is an action on a couple answer verticals on Clank.

Bug: 326368632
Change-Id: I077fcf1d6d184b3a3175eaffd5156640bce288ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5605135


Reviewed-by: Patrick Noland <pnoland@chromium.org>
Commit-Queue: Jennifer Serrano <jennserrano@google.com>
Cr-Commit-Position: refs/heads/main@{#1313050}