Allow annotations to be added to Atom Id

Add atom-level annotations support in StatsEvent.java

setAtomId must be called right after StatsEvent.newBuilder().
Calling setAtomId out of order results in
ERROR_ATOM_ID_INVALID_POSITION.

Bug: 151158793
Test: atest FrameworkStatsdTest
Change-Id: Ib574f079227660193e12b3aa37136d36e154479a