[FIX] website: scroll to the next visible element

Before this commit, the buttons to scroll to the next element might not
work if the next element was invisible.
Steps to reproduce the bug fixed by this commit:

(Note that these steps are only reproducible from 15.0. We decided to
merge this fix in 14.0 to be custo-friendly)

- Install two languages on a website
- Drop a cover block (1), with a height of 100% and a scroll down button
- Drop a new block (2) only visible for language B below the block 1
- Drop a new block (3) visible for everyone below the block 2
- Save and go to the site in language A
- Click on the scroll down button

=> No scroll at all while the user expects to scroll to the block
visible to everyone (3). This commit fixes that by making the user
scroll down to see the next visible element.

opw-2967706

closes odoo/odoo#105334

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