search: fix repository stats for GraphQL search
Created by: tsenart
With the introduction of repo pagination, repository counts changed meaning from the universe of repos to the repositories with matches. While streaming search was straightforward to adjust these statistics to the new semantics, GraphQL wasn't since there are a few different places where we currently cut matches which now need to update or re-compute statistics.
As part of this work, we should introduce a thorough set of integration tests in dev/gqltest/search_test.go for these statistics, both for streaming and GraphQL.