Add Latin script for Manchu (mnc-latn)

Manchu (mnc) should be added to Names.php [1] but the translations are a
mixture of Latin and Mongolian scripts and need to be split [2].
For the autonym, see the existing translations [3] and the main page of the
Manchu Wikipedia in the Incubator [4].

[1] https://phabricator.wikimedia.org/T284043
[2] https://phabricator.wikimedia.org/T318496
[3] https://translatewiki.net/w/i.php?search=%22manju+gisun%22&ns8=1&ns1206=1
[4] https://incubator.wikimedia.org/wiki/Wp/mnc/%E1%A1%A0%E1%A0%B5%E1%A1%A0%E1%A1%B3_%E1%A0%A0%E1%A1%B6%E1%A0%A0%E1%A1%A5%E1%A0%A0

data/language-data.json

@@ -2921,6 +2921,13 @@
             ],
             "ᠮᠠᠨᠵᡠ ᡤᡳᠰᡠᠨ"
         ],
+        "mnc-latn": [
+            "Latn",
+            [
+                "AS"
+            ],
+            "Manju gisun"
+        ],
         "mni": [
             "Mtei",
             [