Isolated exec tests (#11531)

* Run exec tests in fresh contexts

* Reevaluate modules in every context

* Cache module code when running tests

* Eliminate weakmap accesses as much as possible

* Remove old multiline usage

* Using bundled polyfill to significantly increase performance

The individual requires for each file were the part that was sooooo slow.

* Drop LRU cache size

* Fixes

* Fix test

Co-authored-by: Huáng Jùnliàng <jlhwung@gmail.com>

packages/babel-plugin-transform-react-jsx-source/test/fixtures/react-source/basic-sample/exec.js

@@ -3,13 +3,13 @@ var actual = transform(
   Object.assign({}, opts, { filename: '/fake/path/mock.js' })
 ).code;
 
-var expected = multiline([
-  'var _jsxFileName = "/fake/path/mock.js";',
-  'var x = <sometag __source={{',
-  '  fileName: _jsxFileName,',
-  '  lineNumber: 1,',
-  '  columnNumber: 9',
-  '}} />;',
-]);
+var expected = `
+var _jsxFileName = "/fake/path/mock.js";
+var x = <sometag __source={{
+  fileName: _jsxFileName,
+  lineNumber: 1,
+  columnNumber: 9
+}} />;
+`.trim();
 
 expect(actual).toBe(expected);