MDL-66903 core: Introduce \core_component::reset to replace hacks

Traditionally we have done this using reflection and it would be better
to do this in a 'proper' fashion in case we ever need to change how it
works.

lib/classes/component.php

@@ -274,7 +274,6 @@ class core_component {
         return $file;
     }
 
-
     /**
      * Initialise caches, always call before accessing self:: caches.
      */
@@ -399,6 +398,17 @@ class core_component {
         }
     }
 
+    /**
+     * Reset the initialisation of the component utility.
+     *
+     * Note: It should not be necessary to call this in regular code.
+     * Please only use it where strictly required.
+     */
+    public static function reset(): void {
+        // The autoloader will re-initialise if plugintypes is null.
+        self::$plugintypes = null;
+    }
+
     /**
      * Are we in developer debug mode?
      *