Added es3 backward compatibility for react helper code (#10155)

* Added es3 backward compatibility for react helper code

* tweak comment [skip ci]

packages/babel-helpers/src/helpers.js

@@ -26,13 +26,14 @@ helpers.typeof = helper("7.0.0-beta.0")`
   }
 `;
 
+// "for" is a reserved keyword in ES3 so escaping it here for backward compatibility
 helpers.jsx = helper("7.0.0-beta.0")`
   var REACT_ELEMENT_TYPE;
 
   export default function _createRawReactElement(type, props, key, children) {
     if (!REACT_ELEMENT_TYPE) {
       REACT_ELEMENT_TYPE = (
-        typeof Symbol === "function" && Symbol.for && Symbol.for("react.element")
+        typeof Symbol === "function" && Symbol["for"] && Symbol["for"]("react.element")
       ) || 0xeac7;
     }
 

packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/inline-elements/output.js

@@ -1,6 +1,6 @@
 var REACT_ELEMENT_TYPE;
 
-function _jsx(type, props, key, children) { if (!REACT_ELEMENT_TYPE) { REACT_ELEMENT_TYPE = typeof Symbol === "function" && Symbol.for && Symbol.for("react.element") || 0xeac7; } var defaultProps = type && type.defaultProps; var childrenLength = arguments.length - 3; if (!props && childrenLength !== 0) { props = { children: void 0 }; } if (props && defaultProps) { for (var propName in defaultProps) { if (props[propName] === void 0) { props[propName] = defaultProps[propName]; } } } else if (!props) { props = defaultProps || {}; } if (childrenLength === 1) { props.children = children; } else if (childrenLength > 1) { var childArray = new Array(childrenLength); for (var i = 0; i < childrenLength; i++) { childArray[i] = arguments[i + 3]; } props.children = childArray; } return { $$typeof: REACT_ELEMENT_TYPE, type: type, key: key === undefined ? null : '' + key, ref: null, props: props, _owner: null }; }
+function _jsx(type, props, key, children) { if (!REACT_ELEMENT_TYPE) { REACT_ELEMENT_TYPE = typeof Symbol === "function" && Symbol["for"] && Symbol["for"]("react.element") || 0xeac7; } var defaultProps = type && type.defaultProps; var childrenLength = arguments.length - 3; if (!props && childrenLength !== 0) { props = { children: void 0 }; } if (props && defaultProps) { for (var propName in defaultProps) { if (props[propName] === void 0) { props[propName] = defaultProps[propName]; } } } else if (!props) { props = defaultProps || {}; } if (childrenLength === 1) { props.children = children; } else if (childrenLength > 1) { var childArray = new Array(childrenLength); for (var i = 0; i < childrenLength; i++) { childArray[i] = arguments[i + 3]; } props.children = childArray; } return { $$typeof: REACT_ELEMENT_TYPE, type: type, key: key === undefined ? null : '' + key, ref: null, props: props, _owner: null }; }
 
 var _ref =
 /*#__PURE__*/