Paragraph parent entity property is empty when adding new paragraphs

Here's a patch version in addition to the MR.

The fix is pretty simple, we just need to set the paragraph parent entity right after creating the new paragraph but before displaying the edit form.

In using this approach, I found that it is not perfect because $paragraph->getParentEntity() will return NULL on new nodes. getParentEntity() actually loads an entity from the database, and in the event that it's a new node, it's not in the database yet.

However, I found that my patch is still useful because it sets the parent entity type and field name, so I can set up a conditional like this:

function mymodule_form_layout_paragraphs_component_form_alter(&$form, FormStateInterface $form_state) {
    /* @var \Drupal\paragraphs\Entity\Paragraph $paragraph */
  $paragraph = $form['#paragraph'];
  $parent_field_name = $paragraph->get('parent_field_name')->value;
  if ($parent_field_name === 'field_page_content') {
    $form['field_image']['#access'] = FALSE;
  }
}

And it's possible that getParentEntity() may be refactored to store the actual entity instead of loading from the database if 🐛 Cannot access parent entity in hook_entity_create Needs review is completed.