R1:048aa36c236d

Support "-term" in Ferret engine queries

Summary:
Ref T12819. Supports negating search terms, e.g. "apple -honeycrisp".

When negating a term, we're a little more strict about what can match (that is, what can //prevent// a document from being returned) since it's easy for a user to type "apple -honeycrisp -honey -crisp -crispies -olcrispers -honeyyums" to keep refining their search, but hard/impossible to split apart an overboard term.

Test Plan:
- Ran `apple -smith`, `apple -"granny smith"`, etc.