FIX: uses getByIdentifier of d-menu (#611)

The menu service doesn’t implement an activeMenu property anymore as it can now support concurrent menus. The solution to this is to use `getByIdentifier`.

.discourse-compatibility

@@ -1,3 +1,4 @@
+< 3.3.0.beta2-dev: 61890b667c06299841ae88946f84a112f00060e1
 < 3.3.0.beta1-dev: a65c4076a63104b61d213534db7f89aa3c8acd9e
 < 3.2.0.beta5-dev: c70f43f130fb98e4a1adb1afd9b621aaa49088e3
 < 3.2.0.beta4-dev: 493b48477a9288f2f1b6f021954088705a6673d6

assets/javascripts/discourse/connectors/post-text-buttons/ai-helper-options-menu.gjs

@@ -198,7 +198,11 @@ export default class AIHelperOptionsMenu extends Component {
 
     if (option.name === "explain") {
       this.menuState = this.MENU_STATES.result;
-      this.menu.activeMenu.options.placement = "bottom";
+
+      const menu = this.menu.getByIdentifier("post-text-selection-toolbar");
+      if (menu) {
+        menu.options.placement = "bottom";
+      }
 
       const fetchUrl = `/discourse-ai/ai-helper/explain`;
       this._activeAIRequest = ajax(fetchUrl, {