Issue #2316779 by er.pushpinderrana: Fix titles and links in theme/render topics

core/modules/system/core.api.php

@@ -46,7 +46,8 @@
  * - @link cache Caching @endlink
  * - @link utility Utility classes and functions @endlink
  * - @link user_api User accounts, permissions, and roles @endlink
- * - @link theme_render Theme system and render API @endlink
+ * - @link theme_render Render API @endlink
+ * - @link themeable Theme system @endlink
  * - @link migration Migration @endlink
  *
  * @section additional Additional topics

core/modules/system/theme.api.php

 <?php
 
 /**
- * @defgroup themeable Default theme implementations
+ * @defgroup themeable Theme system overview
  * @{
  * Functions and templates for the user interface that themes can override.
  *
@@ -148,12 +148,13 @@
  *
  * @see hooks
  * @see callbacks
+ * @see theme_render
  *
  * @} End of "defgroup themeable".
  */
 
 /**
- * @defgroup theme_render Theme system and Render API
+ * @defgroup theme_render Render API overview
  * @{
  * Overview of the Theme system and Render API.
  *
@@ -222,6 +223,8 @@
  *
  * @todo Check these links. Some are for Drupal 7, and might need updates for
  *   Drupal 8.
+ * @see themeable
+ *
  * @}
  */