Refactor `updateState` and clean up `update3pcState`

This update should make it easier to slot ITP changes / function calls
in within the new switch statement, and makes the overall logic easier
to read by removing one layer of indirection

Change-Id: I584bb620fddda5db9f0419fdebfe31ce2a7de7ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6591742
Reviewed-by: Michelle Abreo <michelleabreo@google.com>
Commit-Queue: Fiona Macintosh <fmacintosh@google.com>
Cr-Commit-Position: refs/heads/main@{#1465989}