Following the new editor's merge at https://github.com/odoo/odoo/pull/29775, 'web_editor.BodyManager' stopped being used by the editor and the related file was moved to website without being renamed or considered. Hopefully, the editor replaced it by something else so the `BodyManager` makes no sense on its own anymore. This commit merges its features with the only other component which still used it: `WebsiteRoot` See upcoming improvements at https://github.com/odoo/odoo/pull/29442 (related to task-1932066) closes odoo/odoo#30740