MDL-64573 output: ajax form event

Add an event that can be fired when an mform is about to be submitted via ajax.
This allows custom field types to perform an action when the form is submitted.

The atto text editor will reset any autosaves when the form is submitted.

lib/editor/tinymce/module.js

@@ -66,6 +66,12 @@ M.editor_tinymce.init_editor = function(Y, editorid, options) {
         editor.onChange.add(function(ed) {
             ed.save();
         });
+        Y.use('event', 'moodle-core-event', function(Y) {
+            var form = Y.one(document.getElementById(editor.id)).ancestor('form');
+            form.on(M.core.event.FORM_SUBMIT_AJAX, function() {
+                editor.save();
+            }, this)
+        });
     };
 
     tinyMCE.init(options);