function greaterThan(propertyName, expression) {
  return new GreaterThan(propertyName, expression);
}
Creates a `<PropertyIsGreaterThan>` comparison operator.

@param {!string} propertyName Name of the context property to compare.
@param {!number} expression The value to compare.
@return {!GreaterThan} `<PropertyIsGreaterThan>` operator.
@api