[FIX] point_of_sale: show pack lot input popup when scanning product

When scanned product is tracked by lot or SN, the popup that asks
for lot should be shown, just like as when a tracked product is clicked
from the product list.

We accomplish this by introducing a new method that can be used both
by `_clickProduct` and `_barcodeProductAction`, and by making the
`_barcodeProductAction` be independent from `scan_product` method
from `PosModel`. So instead of calling directly `scan_product`, we
indentify the product first based on the barcode, then we call the
newly introduced method to ask for the lot inputs, then we call
`add_product` with proper options including the type of the parsed
barcode.

closes odoo/odoo#71209

Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>