search: move SearchResults type out of GQL package
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/30377
moves the type SearchResults definition into package run so we can change the job.Run signature to return this. The many run.SearchResults references created by this change, in the graphqlbackend package, is indicative of logic that we should, and will, move out over time.