Add support for Western Armenian (hyw)

Note that on Wikidata: d:User:Nikki/Permanent duplicates#Armenian, where "hy-arevela" used for Eastern and "hy-arevmda" for Western, because of https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry :

...
%%
Type: variant
Subtag: arevela
Description: Eastern Armenian
Added: 2006-09-18
Prefix: hy
%%
Type: variant
Subtag: arevmda
Description: Western Armenian
Added: 2006-09-18
Prefix: hy
%%
...

Thank you, we are well aware of this subtag which was introduced as an expedient with the knowledge that a formal language code would be required.