[FIX] stock: raise a warning if the user deactivates 'lot & serial numbers' settings while products use it

The "lots & serial numbers" feature can be deactivated at any point.
If there are active products that are tracked, either by lot or serial number,
it can be confusing since deactivating it will hide the relevant fields.
Therefore we raise a warning at onchange if there are tracked active products.

opw 2036173

closes odoo/odoo#35108

Signed-off-by: Nans Lefebvre (len) <len@odoo.com>