AccountManagedStatusFinder: API/terminology cleanup

This CL cleans up the (static) APIs of AccountManagedStatusFinder:
IsKnownConsumerDomain gets inverted to MayBeEnterpriseDomain, and
IsEnterpriseUserBasedOnEmail (returning either "NonEnterprise" or
"Unknown") becomes MayBeEnterpriseUserBasedOnEmail (returning a bool).

This makes the two methods consistent in naming and return type.

Bug: 353880553
Change-Id: Idb10d4d4ffcba00734486ef23a8eb42763f9c469
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5722249
Commit-Queue: Igor <igorcov@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Igor <igorcov@chromium.org>
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1331721}