Discovery Process and Pharmacological Characterization of 2-(S)-(4-Fluoro-2-methylphenyl)piperazine-1-carboxylic Acid 1-(R)-(3,5-Bis-trifluoromethylphenyl)ethylmethylamide (Vestipitant) as a Potent, Selective, and Orally Active NK1 Receptor Antagonist