R1:1d213dc1fa4b

Clean up virtual "_ft_rank" column for query construction of Ferret objects

Summary:
Ref T12974. Ferret object queries SELECT a virtual "_ft_rank" column for relevance ordering.

Currently, they always SELECT this column. That's fine and doesn't hurt anything, but makes developing and debugging things kind of a pain since every query has this `, blah blah _ft_rank` junk.

Instead, construct this column only if we're actually going to use it.

Mostly, this cleans up DarkConsole / query logs a bit.

Test…