Fix article wrapper issue with JSON-LD properties. (#1734)

* Check in post-to-jsonld conversion if post is an entity and expand custom_fields as article type.

* Formatting

src/includes/class-wordlift-entity-type-service.php

@@ -294,7 +294,7 @@ public function set( $post_id, $type_uri, $replace = true ) {
 	 *                             or `$term` was not found.
 	 * @since 3.20.0
 	 */
-	private function get_term_by_slug( $slug ) {
+	public function get_term_by_slug( $slug ) {
 
 		return get_term_by( 'slug', $slug, Wordlift_Entity_Type_Taxonomy_Service::TAXONOMY_NAME );
 	}

src/includes/class-wordlift-post-to-jsonld-converter.php

@@ -96,7 +96,12 @@ public function convert( $post_id, &$references = array(), &$references_infos =
 		// Get the entity name.
 		$jsonld['headline'] = $post->post_title;
 
-		$custom_fields = $this->entity_type_service->get_custom_fields_for_post( $post_id );
+		// Convert entities as `Article`.
+		//
+		// @see https://github.com/insideout10/wordlift-plugin/issues/1731
+		$custom_fields = Wordlift_Entity_Service::get_instance()->is_entity( $post_id )
+			? $this->entity_type_service->get_custom_fields_for_term( $this->entity_type_service->get_term_by_slug( 'article' ) )
+			: $this->entity_type_service->get_custom_fields_for_post( $post_id );
 
 		if ( isset( $custom_fields ) ) {
 			$this->process_type_custom_fields( $jsonld, $custom_fields, $post, $references, $references_infos );