This views has multiple custom features such as file upload, attachment viewer and download. A lot of files have been rendered obsolete and have been deleted, notably `file_upload_mixin` which has been replaced by the file_upload service and hooks. closes odoo/odoo#99769 Related: odoo/enterprise#31145 Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>