Add Vietnamese to Localization Plugin `MapLocale` class

[langsmith]

We support name_vi in Mapbox Streets v8.3.

Seen in Mapbox Studio

The Localization Plugin's MapLocale class could stand to have Vietnamese added to it for convenient access/usage.

https://github.com/mapbox/mapbox-plugins-android/blob/master/plugin-localization/src/main/java/com/mapbox/mapboxsdk/plugins/localization/MapLocale.java#L110-L111

Reference pr is #575 where Japanese and Korean were added to the plugin.

cc as simple fyi @1ec5 @jcsg

[langsmith]

Closing because it's a duplicate of #1098