use get child instead

Author: richardc-db

kernel/kernel-defaults/src/main/java/io/delta/kernel/defaults/internal/data/vector/DefaultVariantVector.java

@@ -82,11 +82,13 @@ public byte[] getMetadata() {
         };
     }
 
-    public ColumnVector getValueVector() {
-        return valueVector;
-    }
-
-    public ColumnVector getMetadataVector() {
-        return metadataVector;
+    @Override
+    public ColumnVector getChild(int ordinal) {
+        checkArgument(ordinal >= 0 && ordinal < 2, "Invalid ordinal " + ordinal);
+        if (ordinal == 0) {
+            return valueVector;
+        } else {
+            return metadataVector;
+        }
     }
 }