*: web_editor Do not display the backdrop element added by bootstrap in the body and add a background on the modal to keep the same effect. The bootstrap backdrop was probably useful for compatibility with <IE9 but is no longer needed. This also avoids z-index issues because modals could be opened in an element (e.g. the website #wrapwrap) whose stacking context is different of the body one (where the backdrop is opened). This would make the backdrop appears on top of the modal. Part of https://github.com/odoo/odoo/pull/49142 Related to task-2229551 Co-authored-by: qsm-odoo <qsm@odoo.com>