Use auto variable declarations for enum iteration

The pattern used in JDK-8257912

  for (vmIntrinsicID index : EnumRange<vmIntrinsicID>{}) {
    nt[as_int(index)] = string;
  }

can be further simplified to the following without loss of readability, since the type of index would be obviously the type enclosed by EnumRange<>

  for (auto index : EnumRange<vmIntrinsicID>{}) {
    nt[as_int(index)] = string;
  }

(as suggested by John Rose)