Complex fields (new UI) creates empty contentNode at JCR for each language

Steps to reproduce

1.  Create a multiValue which has 18n enable, like this:
   myDialog.yaml

   label: Events List
   form:
     properties:
       events:
         $type: jcrMultiField
         i18n: true
         label: Events
         itemProvider:
           $type: jcrChildNodeProvider
         field:
           $type: compositeField
           properties:
             title:
               label: title
               $type: textField
             date:
               label: date
               $type: dateField

1.  Create the component
2. Save data only in English
3. Check at JCR that a mgnl:contentNode (empty) has been created for all available languages

Expected results

Only those nodes of language to which was switched are created. Node for default language is created every time.

Actual results

For each language, a mgnl:contentNode is created, even if the user didn't create (add) any field at the dialog for that language

Workaround

Use the old UI dialog definition (for this case, if you use this you can check the behavior):

form:
  tabs:
    - name: tabText
      label: Multivalue composite
      fields:
        - name: events
          fieldType: multiValue
          i18n: true
          label: Events
          transformerClass: info.magnolia.ui.form.field.transformer.multi.MultiValueSubChildrenNodePropertiesTransformer
          field:
            name: compositeField
            fieldType: composite
            transformerClass: info.magnolia.ui.form.field.transformer.composite.NoOpCompositeTransformer
            fields:
              - name: title
                fieldType: text
                label: Title
              - name: date
                fieldType: date
                label: Date

actions:
  commit:
    class: info.magnolia.ui.admincentral.dialog.action.SaveDialogActionDefinition
  cancel:
    class: info.magnolia.ui.admincentral.dialog.action.CancelDialogActionDefinition

Development notes

On Magnolia 5.7, only those fields which had been added to a language were saved, otherwise they weren't created (please check the attachments)

This behavior affects on first place to performance for users which have lots of languages enabled on a site and, on second place, if working with nodes/delivery api. On that second case, if you perform a REST call to get the nodes for that component you may get (following the Events example) that there are 10 events in 10 different languages when really only English has events and the other 9 are empty nodes that were created because this bug.