src/language-js/utils.js/isObjectTypePropertyAFunction
function isObjectTypePropertyAFunction(node, options) {
  return (
    (node.type === "ObjectTypeProperty" ||
      node.type === "ObjectTypeInternalSlot") &&
    node.value.type === "FunctionTypeAnnotation" &&
    !node.static &&
    !isFunctionNotation(node, options)
  );
}