Refactor test packages to use ES modules instead of CJS (#5138)

packages/babel-plugin-transform-react-jsx-compat/src/index.js

@@ -1,10 +1,12 @@
+import helper from "babel-helper-builder-react-jsx";
+
 export default function ({ types: t }) {
   return {
     manipulateOptions(opts, parserOpts) {
       parserOpts.plugins.push("jsx");
     },
 
-    visitor: require("babel-helper-builder-react-jsx")({
+    visitor: helper({
       pre(state) {
         state.callee = state.tagExpr;
       },

packages/babel-plugin-transform-react-jsx-compat/test/index.js

@@ -1 +1,3 @@
-require("babel-helper-plugin-test-runner")(__dirname);
+import runner from "babel-helper-plugin-test-runner";
+
+runner(__dirname);