convert commit/diff search to job

Created by: camdencheek

This creates the type commit.SearchJob which captures the minimal set of validated arguments for commit and diff search and satisfies the run.Job interface. This cuts out all dependency on search.TextParameters, constructing the job directly from a search query.

This is created in doResults instead of toSearchInputs because it depends on having already resolved the list of repos.

Depends on #25805