[FIX] web: RTL on list view

- Set the user language to a RTL language, e.g. Arabic
- Open a list view containing float or monetary fields, e.g. the invoice
list view

The numbers are left aligned while the corresponding columns headers are
right aligned, making the list view confusing.

The header alignment is hardcoded at rendering rather than in the SCSS.
Therefore, `rtlcss` doesn't affect it.

Instead of hardcoding the alignment, we use a proper CSS class so it is
adapted by `rtlcss`.

opw-2044019

closes odoo/odoo#35414

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>