search: evaluate feature flag datatype early

Created by: rvantonder

Job planner gets a flag set and then calls toFeatures(flagSet *featureflag.FlagSet) search.Features in multiple places to convert it to search.Features. We should do this conversion upfront, even before passing it to the Job planner, because it's only read.

Context: prep for adding feature flag for lucky search, and finding it ugly to have to do this toFeatures(...) thing.

Test plan

Updates tests. Intended to be semantics-preserving. Running against main-dry-run in case we're not setting a non-nil value for this (now pointer) data type.