[FIX] web: allow line return in textareas

Before this commit, textareas in x2many would not allow line return
when pressing enter.

Now, it does.

addons/web/static/src/js/fields/basic_fields.js

@@ -1370,6 +1370,7 @@ var FieldText = InputField.extend(TranslatableFieldMixin, {
      */
     _onKeydown: function (ev) {
         if (ev.which === $.ui.keyCode.ENTER) {
+            ev.stopPropagation();
             return;
         }
         this._super.apply(this, arguments);