[FIX] base_vat: support for 2020 Albanian Tax ID

__Description of the issue this PR addresses:__
The first character of a Tax ID from Albania is a letter representing the decade in which it has been issued. The letter M represents the current decade. (This pdf explains in details how it is formated: https://www.oecd.org/tax/automatic-exchange/crs-implementation-and-assistance/tax-identification-numbers/Albania-TIN.pdf).

Currently the way Albanian Tax IDs are validated is through the python library [`python-stdnum`](https://pypi.org/project/python-stdnum/).
However, the regex that is used to validate them has not been updated since 2017. (I made a PR in its repo arthurdejong/python-stdnum#402 to fix that).

The code from this commit is inspired by the one from that library, but the regex includes the letter M.

__Current behavior before PR:__
(`base_vat` must be installed)
By going to Settings > Users & Companies > [A company]:
- Set the country to Albania
- Set VAT/Tax ID to “M12345678T”.

=> Error message

X-original-commit: f0b6e4c

Author: Dj0ulo

addons/base_vat/models/res_partner.py

@@ -246,6 +246,16 @@ def _build_vat_error_message(self, country_code, wrong_vat, record_label):
             expected_format=expected_format,
         )
 
+    __check_vat_al_re = re.compile(r'^[JKLM][0-9]{8}[A-Z]$')
+
+    def check_vat_al(self, vat):
+        """Check Albania VAT number"""
+        number = stdnum.util.get_cc_module('al', 'vat').compact(vat)
+
+        if len(number) == 10 and self.__check_vat_al_re.match(number):
+            return True
+        return False
+
     __check_vat_ch_re = re.compile(r'E([0-9]{9}|-[0-9]{3}\.[0-9]{3}\.[0-9]{3})(MWST|TVA|IVA)$')
 
     def check_vat_ch(self, vat):