DEAR MISS MANNERS: Manners among theatergoers have been neglected, such that probably most offenders do not even know they are being inconsiderate. The topics of cellphone use, texting, recording, photography, talking, eating, coughing, crackling candy wrappers and even hat wearing have all been covered. But the issue of leaning forward in one’s seat during a performance has been neglected. Theater seats and sight lines were developed with the understanding that patrons would sit with their backs against the seat backs. Leaning forward blocks the view of at least one person in the row behind, …