[docs] Fix imports in External Services examples

These functions have been renamed in Moodle 4.2.

See
- https://web.archive.org/web/20241102043138/https://moodledev.io/docs/4.2/devupdate#external-api
- https://672834180938720008adb671--moodledevdocs.netlify.app/docs/4.2/devupdate#renamed-external-api-classes
- https://moodle.org/mod/forum/discuss.php?d=457297

Author: fapdash

docs/apis/subsystems/external/functions.md

@@ -60,10 +60,10 @@ Please note that deprecation notices will be added to this pathway from Moodle 4
 
 namespace local_groupmanager\external;
 
-use external_function_parameters;
-use external_multiple_structure;
-use external_single_structure;
-use external_value;
+use core_external\external_function_parameters;
+use core_external\external_multiple_structure;
+use core_external\external_single_structure;
+use core_external\external_value;
 
 class create_groups extends \core_external\external_api {
     public static function execute_parameters(): external_function_parameters {

docs/apis/subsystems/external/writing-a-service.md

@@ -145,10 +145,10 @@ This will be located in the file `local/groupmanager/classes/external/create_gro
 <?php
 namespace local_groupmanager\external;
 
-use external_function_parameters;
-use external_multiple_structure;
-use external_single_structure;
-use external_value;
+use core_external\external_function_parameters;
+use core_external\external_multiple_structure;
+use core_external\external_single_structure;
+use core_external\external_value;
 
 class create_groups extends \core_external\external_api {