refactor: Update KeyMapping class to be public.

So aniyomi can access it from the lib directly instead of having to make a copy

app/src/main/java/is/xyz/mpv/KeyMapping.java

@@ -5,7 +5,7 @@
 import android.util.SparseArray;
 import static android.view.KeyEvent.*;
 
-class KeyMapping {
+public class KeyMapping {
     public static final SparseArray<String> map = new SparseArray<>();
 
     static {