Rename keyboard XML files

* Slavic to East Slavic
* Serbian to South Slavic
* Scandinavian to Nordic

Bug: 6150183
Change-Id: I8f5641aa07b83cbb225f5fd73e351a6f8abe0784
diff --git a/java/res/values/attrs.xml b/java/res/values/attrs.xml
index 7758074..5720a9a 100644
--- a/java/res/values/attrs.xml
+++ b/java/res/values/attrs.xml
@@ -388,6 +388,7 @@
         <attr name="parentStyle" format="string" />
     </declare-styleable>
 
+    <!-- TODO: Should be removed. This is no longer required if InputMethodSubtype is supported. -->
     <declare-styleable name="KeyboardSet">
         <!-- Locale of the keyboard layouts -->
         <attr name="keyboardLocale" format="string" />