A Phase 3, Multicenter, Randomized, Double-blind, Placebo-controlled, Study to Compare the Efficacy and Safety of Triple Therapy (Oral Treprostinil, Ambrisentan, and Tadalafil) With Dual Therapy (Ambrisentan, Tadalafil, and Placebo) in Subjects With Pulmonary Arterial Hypertension - ICH GCP - Clinical Trials Registry