R1:3b43a7077345

Add "title:..." support to the Ferret engine

Summary:
Ref T12819. Adds (hacky, hard-coded) field support (for now, only for "title").

I've written this so `title:quick ferret` is the same as `title:quick title:ferret`. I think this is what users probably mean.

You can do the other thing as `ferret title:quick`, or `title:quick all:ferret`.

Test Plan: Searched for `title:x`, `title:"x"`, `title:~"x"`, etc. Searched for "garbage:y", got an exception since that's not a recognized function. Searched for…