search: use reposet to reduce work in indexed repohasfile filtering

Created by: keegancsmith

Currently we search all indexed repositories on zoekt when filtering with repohasfile. However, we can reduce that work and only search within the current reposet.

On large instances this should increase performance whenever we are dealing with a subset of all repos. This is quite common if a user does not have permission to access all repositories. Additionally when a query contains a repo filter or multiple repohasfile filters this will reduce the work done.

Part of https://github.com/sourcegraph/sourcegraph/issues/7380