search: unify calls to zoektIndexedRepos and zoektSearchHEAD
Created by: keegancsmith
Currently the clients of zoekt need to first call zoektIndexedRepos, make some adjustments based on arguments, then call zoektSearchHEAD. We abstract out these details into a single structure indexedSearchRequest.
This also makes it possible for us to maintain more state between the call from zoektIndexedRepos to zoektSearchHEAD. The main need for this is to maintain which branch is for which repository revision when interpreting results from Zoekt. This will be done in another PR.
Note all the duplication between symbols and text search. This was mostly removed in this commit.