MDL-71573 qbank_exportquestion: Add plugin to core

This implementation will introduce a qbank plugin "exporquestions"
which will add the export feature in the question bank view
by replacing the core classes. Having this plugin will give users
the flexibility of enabling or disabling the export questions tab.

Co-Authored-By: Guillermo Gomez Arias <[email protected]>

question/export_form.php

@@ -34,10 +34,15 @@ require_once($CFG->libdir . '/formslib.php');
  *
  * @copyright  2007 Jamie Pratt [email protected]
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @deprecated since Moodle 4.0 MDL-71573
+ * @see qbank_exportquestions\form\export_form
  */
 class question_export_form extends moodleform {
 
     protected function definition() {
+        debugging('Class question_export_form in \core_question\export_form is deprecated,
+        please use core_question\bank\exportquestions\export_form instead.', DEBUG_DEVELOPER);
+
         global $OUTPUT;
 
         $mform = $this->_form;