Add a new UserNameUtils service

This replaces User::isValidUserName, ::isUsableName, ::isCreatableName,
::getCanonicalName, and ::isIP.

Unlike User::isIP, UserNameUtils::isIP will not return true
for IPv6 ranges.

UserNameUtils::isIPRange, like User::isIPRange, accepts a name and
simply calls IPUtils::isValidRange.

User::isValidUserName, ::isUsableName, ::isCreatableName,
::getCanonical, ::isIP, and ::isValidRange are all soft deprecated

A follow up patch will add this to the release notes, to avoid merge
conflicts.

Bug: T245231
Bug: T239527
Change-Id: I46684bc492bb74b728ff102971f6cdd4d746a50a