Add "use strict" directive (#7411)

* #7349
- Add "use strict" directive to transformed class bodies

* Update tests (#7349)

* Add test for program with use strict directive (#7349)

* Update tests (#7349)

* Update source mapping (#7349)

* Add test for parent blockStatement with use strict directive (#7349)

* Update tests (#7349)

* Update tests (#7349)

* Update tests (#7349)

* Add test for constructor-only class (#7349)

* Constructor only classes are strict, too

But constructor only that use non-simple parameters must use a strict function wrapper.

* Fix test

* Wrapper not needed if class is already strict

* Revert change to lerna.json

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

@@ -9,6 +9,8 @@ var _ref =
 let App =
 /*#__PURE__*/
 function (_React$Component) {
+  "use strict";
+
   babelHelpers.inherits(App, _React$Component);
 
   function App() {