[REF] website, web_editor: refactor (quotes) carousel snippets

Previously, the carousel and quotes carousel snippets were the only ones
that were not enclosed in section blocks. This had a number of
undesirable side effects, such as editing the anchor on the carousel
breaking the carousel functionality, and the inability to separately
choose a background for the carousel itself and individual slides.

I also used this opportunity to move controls relative to the entire
carousel onto the carousel itself rather than the individual slides. The
sizing_y (vertical padding) will however keep targeting individual
slides, as the carousel uses the height of its tallest slide, and also
because padding on the carousel will not get covered by slide
backgrounds and saty blank, which is unwanted.

Lastly, most of the snippet options for the carousel were rewritten, as
they were quite broken. There was some compatibility code for saas-3
left, some useless events were bound to the controls, even though they
were already handled through event-delegation at the document level.
Finally, most of the edition features were broken on duplicated
carousels since the onClone method wasn't reassigning most of the things
it needed to.

Part of https://github.com/odoo/odoo/pull/38997
task-2090180