[FIX] sale: correct ordering of onchange updates

Since e9ad3442, on product change,
the uom & qty were only reset to defaults after the price & tax
recomputation.

This commit brings back the previous (and correct) behavior, by updating
the uom & qty alongside the description, before the taxes & price updates.

closes odoo/odoo#121883

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>
Co-authored-by: Duong Kim <81897633+kimduong986@users.noreply.github.com>