Use CodeMirror twig ?

Hello,

On a symfony 3.4 with KMS Froala 2.9.8 i'm tring to use Twig : https://codemirror.net/mode/twig/index.html

```
$builder->add('twigContent', FroalaEditorType::class, array('codeMirrorOptions' => array(
'indentWithTabs' => true,
'lineNumbers' => true,
'lineWrapping' => true,
'mode'=> array('name' => "twig", 'base' => "text/html"),
'tabMode' => 'indent',
'tabSize' => 2
)
, 'label' => 'Contenu', 'attr' => array('class' => 'froalaMailTransTemplate', 'id' => 'froalaMailTransTemplate'), 'required' => false))
```

if i remove the code `'mode'=> array('name' => "twig", 'base' => "text/html")` it's working i have HTML but no "twig" markup

What did i miss ?

thanks

Guldil

Start by inspecting FroalaEditorType and how its codeMirrorOptions load and select CodeMirror modes, then reproduce the Symfony 3.4 configuration with the Twig mode from the linked CodeMirror page. Done means Twig markup is highlighted while the existing HTML editing behavior still works.

Written by the indexing model from the issue text.