Review the layout to always use standard bootstrap classes so that
future task targeting modal can target s_popup snippets the same way
(for example: our task allowing to open a popup on click on a button).
This also allows to simplify the css and simplify the options. A new
option also now allows to have a backdrop, or not, so that user clicks
are blocked while the popup is opened, or not.
+ Adapt cookie bar accordingly.
Part of https://github.com/odoo/odoo/pull/52698
task-2210730
Co-authored-by: qsm-odoo <qsm@odoo.com>
