Member predicate PropertyProjection::isSingletonProjection

Holds if this call returns the value of a single projected property, as opposed to an object that can contain multiple projected properties.

Examples:

• This predicate holds for _.get({a: 'b'}, 'a'), which returns 'b',
• This predicate does not hold for _.pick({a: 'b', c: 'd'}}, 'a'), which returns {a: 'b'},