Angiotensin‐II Analogues. I: Synthesis and incorporation of the halogenated amino acids 3‐(4′‐iodophenyl)alanine, 3‐(3′,5′‐dibromo‐4′‐chlorophenyl)alanine, 3‐(3′,4′,5′‐tribromophenyl)alanine, and 3‐(2′,3′,4′,5′,6′‐pentabromophenyl)alanine