[FIX] web_editor: ensure powerbox gets selection from owner document

When checking if the powerbox should open, we check the selection but
that was done on the global document, which returns a wrong selection
for the editable if it's in an iframe. As a result, the powerbox never
opened in mass_mailing.

task-2778414

closes odoo/odoo#85352

X-original-commit: d5b8c26c46b1daf795a6b286af80bb4dad8072ff
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Signed-off-by: Antoine Guenet <age@odoo.com>

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -109,7 +109,7 @@ const Wysiwyg = Widget.extend({
             getYoutubeVideoElement: getYoutubeVideoElement,
             getContextFromParentRect: options.getContextFromParentRect,
             getPowerboxElement: () => {
-                const selection = document.getSelection();
+                const selection = (this.options.document || document).getSelection();
                 if (selection.isCollapsed && selection.rangeCount) {
                     const node = closestElement(selection.anchorNode, 'P, DIV');
                     return !(node && node.hasAttribute && node.hasAttribute('data-oe-model')) && node;