As part of the work on SERVER-35493, we unified the majority of the logic for InclusionNode and ExclusionNode into a ProjectionNode base class. Because this class must agnostically support any projection type, inclusions now write to the output document using MutableDocument::setField rather than MutableDocument::addField, since exclusions cannot use addField. For large inclusion projections, however, this introduces a per-field performance hit, as setField's lookup-and-replace behaviour is slower than addField's straightforward append.