[FIX] website, *: hide .s_popup itself too, not only its .modal child

*: website_mass_mailing (tests)

- Web Editor facts:
Since the refactoring of the editor done at [1], the cookies bar popup
is receiving a `contenteditable=true` attribute, making it receive the
chrome default `height` style for such elements.
The problem is that if this cookies bar's modal is hidden, the bar will
be shown as a thin empty white bar.

- Website Builder / Popup Snippet / Cookies bar facts:
A popup element is composed of a `.s_popup` parent containing the actual
`.modal` BS modal. Our internal logic and events are hiding and showing
this inner `.modal` modal element without considering its `.s_popup`
parent. It means that when the `.modal` is hidden, its `.s_popup` parent
is not touched and kept visible.
It might looks like it's not an issue as it would just be an empty
element (its only child is hidden) but it leads to some issues as
explained just above: an ugly white bar is shown.
Note that the cookies bar is nothing more than a `.s_popup` snippet.

- Web Editor facts 2:
During the mentioned refactoring [1], they actually added some code to
hide this bug once you were playing with the edit mode (mainly for when
you clicked on the invisible panel element or before saving).
But this code was actually not fixing the case when you just entered
edit mode.

This commit simply remove that "edit only" web editor logic and add a
new one in charge of simply synchronizing the `.s_popup` snippet
visibility with its `.modal` BS modal in a public widget (which is
obviously also executed in edit mode).

Finally:
- note that if there is no way through regular flow to arrive to the
  same result with a normal popup snippet, it is still concerned by this
  issue and you can reproduce it by moving it somewhere else in the DOM
  and/or simply adding it the `contenteditable=true` attribute.
- we already fixed that issue a few months/years ago, I couldn't find
  a commit related to that so I don't know if it was due to the same
  root cause
- in case one is wondering why we simply couldn't do that in the already
  existing `_onHideModal` of the `PopupWidget`, it is because that
  `hide.bs.modal` is not called when entering edit mode, because the
  `destroy` is destroying it before hiding the modal. The event is thus
  not fired. And we can't move the hide part before the destroy's super
  because otherwise, it would go through the normal hidden process which
  is creating a "seen" cookie for the popup as if it was closed
  manually.

[1]: https://github.com/odoo/odoo/commit/740168ce8d27da3d6a7156d2d79655a898394923



task-2754108

closes odoo/odoo#103382

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>