code: int getFieldIndex(TypeElement declaringClass, String name, String descriptor)
      {
          String fullyQualifiedForm = declaringClass.getQualifiedName().toString();
          return getRefIndex(Fieldref.class, fullyQualifiedForm, name, descriptor);
      }
docs: Returns the constant map index to field
  @param declaringClass
  @param name
  @param descriptor
  @return