[FIX] website: fix contradiction between visibility class and height

Before this commit, when a snippet section was hidden on mobile devices
and its height was then set to 50% or 100%, the visibility classes
remained as "d-lg-block" instead of "d-lg-flex". This inconsistency
resulted in the content not being vertically centered until the "hidden
on mobile" toggle was turned off and then back on.

Steps to reproduce the bug:
- In edit mode, drag and drop a "Text" snippet onto the page.
- Click on the "Mobile visibility" option button to hide the snippet on
mobile devices.
- Click on the "50%" button in the "Height" option of the snippet.
- Bug: The content within the "Text" snippet is not vertically centered.

This commit fixes the issue by properly updating the CSS class set by
the mobile visibility option when the "height" option is enabled.

task-3224575

closes odoo/odoo#121434

Signed-off-by: Bojabza Soukéina (sobo) <sobo@odoo.com>