Deduplicate discrete operation before delivering result.

Before returning result from the API, we go through the list
of all AttributedOpEntries and those which have the same
timestamp are merged into single AttributedOpEntry without
losing any information (it is still possible to query
AttributedOpEntry with different flags / uidstates and get
all the same information).

This CL addresses issue with duplication due to accesses
with different flags / uidstates.

Test: in development
Bug: 176965672
Bug: 183961838
Change-Id: I319dd321a3bfddf0855c10213c49824e9599eb66