[FIX] various: not translate the close icon of notifications

Same change in several areas where translations existed:
- website editor notification popup
- elearning share popup
- forum remediation filter popup
- event registration attendees popup
- portal rating popup
- stripe payment error popup
And many other locations where there were no translations yet
"×" has been replaced by its UTF8 character.
Also introduced aria-label where missing.

Before this commit the close icon was included in translated resources.
For example, in Spanish the "×" had been turned into "&veces;"
thus not rendering an icon anymore

After this commit the close icon is not a translated text anymore and
remains an icon across all languages

https://github.com/odoo/odoo/pull/60186


task-2312878

closes odoo/odoo#60186

Related: odoo/enterprise#14209
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>