If by definition you are trying to determine what helicopter was first with some sort of stabilization then it was an HO3S1-G in the US Coast Guard around 1949 or possibly earlier. What they did was attach an airfoil to the swashplate, which stabilized the swashplate in any position the pilot set it in. In the configuration of that HO3S the flight controls had jackscrews which had some degree of reversibility which allowed feedback to the cyclic. The airfoil helped to dampen the feedback forces by stabilizing the swashplate.
