[FIX] web_editor: display drop zones only on dropdowns when shown

It was painful to add an inline snippets, or move elements inside mega
menus. The dropdowns are now behaving as modals: if they are shown, the
user can only add or move snippets inside them, but not outside.

task-2668908

closes odoo/odoo#80757

X-original-commit: edc5c8d69fb5fc6da0b0012abc6539c21ffc421e
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/editor/snippets.editor.js

@@ -1568,11 +1568,16 @@ var SnippetsMenu = Widget.extend({
     _activateInsertionZones: function ($selectorSiblings, $selectorChildren) {
         var self = this;
 
-        // If a modal is open, the drop zones must be created only in this modal
-        const $openModal = self.getEditableArea().find('.modal:visible');
-        if ($openModal.length) {
-            $selectorSiblings = $openModal.find($selectorSiblings);
-            $selectorChildren = $openModal.find($selectorChildren);
+        // If a modal or a dropdown is open, the drop zones must be created
+        // only in this element.
+        const $editableArea = self.getEditableArea();
+        let $open = $editableArea.find('.modal:visible');
+        if (!$open.length) {
+            $open = $editableArea.find('.dropdown-menu.show').addBack('.dropdown-menu.show').parent();
+        }
+        if ($open.length) {
+            $selectorSiblings = $open.find($selectorSiblings);
+            $selectorChildren = $open.find($selectorChildren);
         }
 
         // Check if the drop zone should be horizontal or vertical