Update codeintel db package for worker

Created by: efritz

Add additional methods to teh codeintel db package that will be needed by the precise-code-intel-worker.

This partially implements https://github.com/sourcegraph/sourcegraph/issues/9965.

Created by: codecov[bot]

Codecov Report

Merging #10227 into master will decrease coverage by 0.38%. The diff coverage is 73.74%.

@@            Coverage Diff             @@
##           master   #10227      +/-   ##
==========================================
- Coverage   44.04%   43.66%   -0.39%     
==========================================
  Files        1419     1396      -23     
  Lines       77891    76800    -1091     
  Branches     6706     6706              
==========================================
- Hits        34310    33533     -777     
+ Misses      40430    40199     -231     
+ Partials     3151     3068      -83     

Flag	Coverage Δ
#unit	43.66% <73.74%> (-0.39%)

Impacted Files	Coverage Δ
internal/codeintel/db/db.go	43.75% <0.00%> (-4.53%)
internal/codeintel/db/scan.go	79.31% <ø> (ø)
internal/codeintel/db/job_handle.go	53.06% <53.06%> (-3.35%)
internal/codeintel/db/packages.go	83.01% <67.85%> (-1.20%)
internal/codeintel/db/uploads.go	85.63% <81.57%> (-2.55%)
internal/codeintel/db/dumps.go	89.38% <90.00%> (-1.74%)
internal/codeintel/db/references.go	79.74% <90.00%> (-3.59%)
internal/codeintel/db/commits.go	90.90% <90.90%> (+2.02%)
... and 27 more