Chiral Phosphoric Acid Catalyzed (4 + 1) Annulation of 3‐Diazooxindoles/4‐Diazooxisoquinolines with para‐Quinone Methides to Access Chiral Spiro[dihydrobenzofuran‐2,3'‐oxindoles/2,4'‐oxisoquinolines]