[FIX] web_editor: disable embedded video for html fields in backend

TLDR: the videos doesn't work anyway, but nobody noticed it for years; at the
same time there is no easy way to fix it

STEPS:

* create a record with html field, e.g. project.task
* add an embedded video (File/Image icon)
* save

BEFORE: video doesn't work

AFTER: there is no option to add embedded video anymore

WHY:

* iframe tags are removed before storing html in database, so after saving a
record, embedded video doesn't work anymore
* possible fixes look too tricky for stable branches:

  * new field attribute sanitize_iframe=False -- requires changes in core python framework which may have side effect

  * adding iframe on client side -- the problem is that the backend doesn't
  have mechanism to use animation in html fields like it's done in
  website: https://github.com/odoo/odoo/blob/ced500e9bcbb5c84033463689d135ad4c7dc4f39/addons/website/static/src/js/content/snippets.animation.js#L623-L632

  * adding iframe on server side -- parsing html fields in _read... Doesn't look good either

* double selector is required to make it work both in frontend and backend:

      $editable.closest('.o_editable, .note-editor')

* we don't need hardcoded exception for mailing.mailing, mail.compose.message
because those fields marked as sanitized (default value)

  https://github.com/odoo/odoo/blob/c92f058571b0656451f24e24154dd1bdb3bdb48a/odoo/fields.py#L1589-L1590
  https://github.com/odoo/odoo/blob/c92f058571b0656451f24e24154dd1bdb3bdb48a/addons/mail/wizard/mail_compose_message.py#L115
  https://github.com/odoo/odoo/blob/61734cdaf1cf6857125b1ece63928ab080359c6c/addons/mass_mailing/models/mailing.py#L77



* I don't apply this for Odoo 12, because js is refactored in Odoo 13 (e.g.
field_html.js has another name in Odoo 12)

---

opw-2353103

closes odoo/odoo#60418

Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>