Add the Dargin (Dargwa) language (dar)

Requested at
https://translatewiki.net/wiki/Thread:Support/Dargin_language

Autonym according to:
Х.ГӀ. Юсупов, «Даргала-урусла словарь», ХӀ. ЦӀадасала уличилси
Мезла, литературала ва искусствола институт, МяхIячкъала 2014
and verified with speakers.

data/language-data.json

@@ -894,6 +894,13 @@
             ],
             "dagbanli"
         ],
+        "dar": [
+            "Cyrl",
+            [
+                "EU"
+            ],
+            "дарган"
+        ],
         "de-at": [
             "Latn",
             [
@@ -5705,6 +5712,7 @@
             "os",
             "kbd",
             "myv",
+            "dar",
             "mdf",
             "kum",
             "kv",