search: use type:repo for repohasfile queries

Created by: keegancsmith

Previously we would search zoekt to narrow down the set of repositories to search for each repohasfile token. However, we can instead directly create a zoekt query which captures the same meaning. By directly creating the query we can remove our application level filtering we do.

This change is motivated by multiple branch search. The reposet code is unaware of branches and makes it difficult to adapt to branches.

Note: I have duplicated the logic for structural search's HandleFilePathPatterns. Structural search is already duplicating logic, so I am following the pattern. I will soon investigate how to potentially remove the duplication in structural search.

Note: type:repo is a Sourcegraph specific extension to Zoekt.