[FIX] web_editor: properly handle (responsive) images

This addresses a series of issues regarding images, their responsive
behavior and their alignment.

This is a partial backport of commit [1] from 16.0.

[1]: https://github.com/odoo/odoo/commit/25f63ecdc89cfabe07f0348c1dc5c830aeed7cca

Part-of: odoo/odoo#125146