[FIX] web: use language week_start in datepickers

Before this rev., if the week_start param (the first day of week)
of the user language was changed, it wasn't reflected on datepickers
(however, it worked fine in the calendar view). This rev. makes this
work by updating the moment locale with the corresponding param.

Fixes #36450
Closes #36532

closes odoo/odoo#38398

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>