Move the implement of getAllCollapsedRatTypes to StatsPullAtomService

To make data usage as a mainline module, move getAllCollapsedRatTypes
to StatsPullAtomService since currently it is the only user. Also, the
method needs to call getCollapsedRatType, thus move getCollapsedRatType
to NetworkStatsManager and expose it as module API.

Bug: 210073043
Test: builds, FrameworksNetTests
Change-Id: Ibe41b50f173464694c21dd22841552bdb69a6a14