Record Experiments oped-in to status

Some refactoring to the handler code as well.
The refactoring ensures that compile errors are triggered
if new promo types or actions are added.

Bug: b:283540965
Change-Id: I211441a9d4086ee030f3e3dd22eb649e1d87b2f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4550200


Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147323}