[Code Health] Move PredictionGrantLikelihood into PermissionUiSelector

The PredictionGrantLikelihood typedef was defined inside
`PermissionUmaUtil`, but it is used in many locations that are unrelated
to that class. Moving the definition to `PermissionUiSelector` make it
more obvious where it comes from.

Bug: 429572321
Change-Id: I35b75a5acd01a02e292e49afa3eff9e7c0782f97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6700778
Reviewed-by: Sun Yueru <yrsun@chromium.org>
Reviewed-by: Judith Hemp <hempjudith@google.com>
Commit-Queue: Elias Klim <elklm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1482674}