Add Browserslist javascripts environment for JavaScripts

We’re using Safari 11 as a minimum so that checks for `nomodule` will also pass

```
'noModule' in HTMLScriptElement.prototype
```

Using the query `> 0.1% in GB` unintentionally brings in Safari on iOS 8.1-8.4, 9.3 with only Safari 9+ supporting ES2015 modules, and Safari 11+ supporting `nomodule`

docs/examples/webpack/.browserslistrc

@@ -7,6 +7,16 @@ Firefox ESR
 Safari >= 12
 iOS >= 12.1
 
+[javascripts]
+> 0.1% in GB and supports es6-module
+last 6 Chrome versions
+last 6 Firefox versions
+last 6 Edge versions
+last 2 Samsung versions
+Firefox ESR
+Safari >= 12 and not Safari < 11
+iOS >= 12.1 and not iOS < 11
+
 [stylesheets]
 > 0.1% in GB and not dead
 last 6 Chrome versions

docs/examples/webpack/babel.config.js

@@ -5,7 +5,7 @@
  */
 module.exports = function (api) {
   const browserslistEnv = !api.env('test')
-    ? 'production'
+    ? 'javascripts'
     : 'node'
 
   return {

packages/govuk-frontend-review/.browserslistrc

@@ -7,6 +7,16 @@ Firefox ESR
 Safari >= 12
 iOS >= 12.1
 
+[javascripts]
+> 0.1% in GB and supports es6-module
+last 6 Chrome versions
+last 6 Firefox versions
+last 6 Edge versions
+last 2 Samsung versions
+Firefox ESR
+Safari >= 12 and not Safari < 11
+iOS >= 12.1 and not iOS < 11
+
 [stylesheets]
 > 0.1% in GB and not dead
 last 6 Chrome versions

packages/govuk-frontend/.browserslistrc

@@ -10,6 +10,16 @@ Firefox ESR
 Safari >= 12
 iOS >= 12.1
 
+[javascripts]
+> 0.1% in GB and supports es6-module
+last 6 Chrome versions
+last 6 Firefox versions
+last 6 Edge versions
+last 2 Samsung versions
+Firefox ESR
+Safari >= 12 and not Safari < 11
+iOS >= 12.1 and not iOS < 11
+
 [stylesheets]
 > 0.1% in GB and not dead
 last 6 Chrome versions