Optimize the rule dependency search query.
Optimize the rule dependency search query.

 - This adds an additional covering index for the rule dependency query, which
   is important for the null build case where our work largely amounts to
   populating and scanning the results.

 - This fixes a regression introduced in
   bcc3d1011eff6450d74f9b0bec913d17bf48efa2 -- the table primary key index was
   previously covering, but now is not because of the required ordinal
   parameter.

 - This change is unfortunate as there is a lot of redundancy in the tables, and
   this increases database size by 25% in one example, but it is also good for a
   ~10% win in null build time on a large graph.

 - <rdar://problem/32127527> Investigate optimizing rule dependency w/ ordinal lookup

apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild,apple/swift-llbuild