Updates the histogram with new ThirdPartyCookieAllowMechanism

This CL:
- Segments ThirdPartyCookieAllowMechanism::kAllowBy3PCDMetadata into:
  ThirdPartyCookieAllowMechanism::kAllowBy3PCDMetadata,
  ThirdPartyCookieAllowMechanism::kAllowBy3PCDMetadataSource1pDt,
  and ThirdPartyCookieAllowMechanism::kAllowBy3PCDMetadataSource3pDt.

- Makes changes to the test helpers to allow for source field setup.

- Fixes Enum label mismatch introduced at https://chromium-review.googlesource.com/c/chromium/src/+/5201726/9/tools/metrics/histograms/metadata/page/enums.xml

- Creates a new mojom to hold content setting enums single source of truth definitions following https://chromium.googlesource.com/chromium/src/+/HEAD/docs/security/mojo.md#using-mojo-enums-directly-when-possible

OBSOLETE_HISTOGRAMS=histogram PageLoad.Clients.TPCD.CookieAccess.ThirdPartyCookieAllowMechanism is replaced by PageLoad.Clients.TPCD.CookieAccess.ThirdPartyCookieAllowMechanism2

Followup: Migrate the other enums to the new mojom and get rid of duplicate enums defs.

Change-Id: Ia8a8052117af7c2b1316a81e3c3a4fd1a1954007
Bug: b:324070923
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5280542


Auto-Submit: Jonathan Njeunje <njeunje@chromium.org>
Reviewed-by: Chris Fredrickson <cfredric@chromium.org>
Reviewed-by: mmenke <mmenke@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1261575}