[FIX] web_editor, website: allow autoplay of youtube videos on mobile

The autoplay option for youtube videos in a .media_iframe_video snippet
does not currently work on mobile devices. This happens because the
autoplay param in the url is only considered for desktop devices.

Mobile autoplay can be forced by using the youtube js api, in the same
way as it is already done for background videos. Therefore, the common
code is extracted into a mixin, extended by both widgets.

opw-2607308

closes odoo/odoo#87912

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>