search: move lucky search out of jobutil
Created by: rvantonder
Stacked on https://github.com/sourcegraph/sourcegraph/pull/38692.
Moves lucky search into internal/search/lucky
. Reasonable? Anticipating Rok may want to extend/modify things too, not sure if that will continue living in internal/search/lucky
or internal/search/nlp
or something, but all the more reason to move more logic out of jobutil.
Test plan
Semantics-preserving.