[FIX] website, web_editor: allow to re-edit social media icons

This commit allows you to change the icons of custom links of the social
media block after the first save. Thanks to [this other commit], there
is now a class that permits to inform the editor that a media is
editable even if it is a non-editable parent. This commit permits to use
the new class to fix the issue.

Steps to reproduce the bug:
- Drop a social media block on a page
- Add a custom social media
- Save
- Edit
- Try to change the icon of the custom social media with a double-click

=> The icon cannot be changed.

Note that [another commit] had already been made and fixed the problem
halfway (the icon change didn't work on double-click). This commit
reverts it and fixes the problem correctly with the new system.

[this other commit]: https://github.com/odoo/odoo/commit/6ead397f33512c918f51feb2b32fb3e15ffedf34
[another commit]: https://github.com/odoo/odoo/commit/bb291b35e46e42ca098aa3e04ac0b473f72be423

Fixes https://github.com/odoo/odoo/issues/104048
task-3073171

X-original-commit: https://github.com/odoo/odoo/commit/a46a8f45b65ca9ecfbb12ffb7980902085666e1a
Part-of: odoo/odoo#133860