[FIX] mass_mailing: ensure no lazy loaded images on edit start

If images are lazy loaded in mass_mailing they risk not being converted
properly. This removes the loading attribute from all previously added
images when the editor loads.

opw-2850967

closes odoo/odoo#98107

X-original-commit: 3cb0f466cfa982aeb802e08ded8bdbf7b8f01220
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Signed-off-by: Antoine Guenet (age) <age@odoo.com>

addons/mass_mailing/static/src/js/mass_mailing_widget.js

@@ -160,6 +160,11 @@ var MassMailingFieldHtml = FieldHtml.extend({
         }
         return this._super.apply(this, arguments);
     },
+    _createWysiwygInstance: async function () {
+        const res = await this._super(...arguments);
+        this.wysiwyg.getEditable().find('img').attr('loading', '');
+        return res;
+    },
 
     /**
      * @override