docs: public static String getJsExtensionImport(FieldDescriptor desc) {
      Descriptor scope = desc.getExtensionScope();
      if (scope != null) {
        while (scope.getContainingType() != null) {
          scope = scope.getContainingType();
        }
        return calculateQualifiedJsName(scope);
      }
      return getJsPackage(desc.getFile()) + "." + computeJsExtensionName(desc);
    }