search: refactor to use a type for resolved repo values

Created by: rvantonder

I wanted to do things with determineRepos and decided the multivalue return is too much. I made a new type resolvedRepositories to hold these values and propagated the values in this type. So this is a mechanical refactor. However: this PR is split into two commits because the first commit I feel confident about, the second one deserves a bit more attention because it touches caching code (both are still intended to be completely mechanical).

Note on variable choice: initially I called the return value result in some places, but when it started conflicting with other variables in other functions that already used result, I opted to just use the name resolved everywhere. This PR also fixes a lot of inconsistent naming (like repoRevs versus repositoryRevision versus repos all used for the same value).