Add Campidanese Sardinian (sro)

Requested for translatewiki at
https://translatewiki.net/wiki/Thread:Support/Request_for_Campidanese_(sro)_qualification

Autonym according to
Giovanni Melis,
"Fueddariu Sardu Campidanesu - Italianu",
Selargius, 2004

data/langdb.yaml

@@ -598,6 +598,7 @@ languages:
   sr-el: [sr-latn]
   sr-latn: [Latn, [EU], srpski]
   srn: [Latn, [AM, EU], Sranantongo]
+  sro: [Latn, [EU], sardu campidanesu]
   ss: [Latn, [AF], SiSwati]
   st: [Latn, [AF], Sesotho]
   stq: [Latn, [EU], Seeltersk]

data/language-data.json

@@ -3870,6 +3870,13 @@
             ],
             "Sranantongo"
         ],
+        "sro": [
+            "Latn",
+            [
+                "EU"
+            ],
+            "sardu campidanesu"
+        ],
         "ss": [
             "Latn",
             [