base_vat_optional_vies: Migrate deprecated `vatnumber` to `python-stdnum` library

[moylop260]

To fix the runboat install issue we need to get rid of the vatnumbers dependency in favor of python-stdnum. vatnumber is obsolete and does not install anymore with a recent toolchain. Odoo does not use it anymore in v14.

Originally posted by @sbidoul in #1695 (comment)

Issue related: #1699
Quick-fix PR to fix all the runboat builds 14.0: #1700

But the final solution must be migrate the module base_vat_optional_vies to use python-stdnum library

[moylop260]

Feel free to create a new PR to use be compatible with latest version of vatnumber