Currently, all of the index key generation files owned by query execution reside in 'src/mongo/db/index'. To more clearly group these together by component and for ownership purposes, this ticket proposes moving all of these files to a common directory, that is, something like:

src/mongo/db/query/key_generation
src/mongo/db/index/key_generation
src/mongo/db/query/write_ops/key_generation