[incremental] expose more metrics fields

Exposing more data loader states as per
go/incremental-crash-reports-1-pager.

BUG: 184844615
Test: atest service.incremental_test
Test: atest android.cts.statsdatom.incremental.AppErrorAtomTests
Change-Id: I532513453411b2ccdb21311d0bc3dee0641837db