Issue #3229714 by paul121: Correct visibility of getPluginDefinition function...

Issue #3229714 by paul121: Correct visibility of getPluginDefinition function in ContextAwarePluginTrait

(cherry picked from commit c636d19c)

core/lib/Drupal/Core/Plugin/ContextAwarePluginTrait.php

@@ -150,7 +150,7 @@ public function setContextMapping(array $context_mapping) {
   /**
    * {@inheritdoc}
    */
-  abstract protected function getPluginDefinition();
+  abstract public function getPluginDefinition();
 
   /**
    * {@inheritdoc}