code: public static String shardedLinkTermRowKey(FieldDefinition linkDef, String objID, int shardNumber) {
          assert linkDef.isLinkField() && linkDef.isSharded() && shardNumber > 0;
          StringBuilder shardPrefix = new StringBuilder();
          shardPrefix.append(shardNumber);
          shardPrefix.append("/");
          shardPrefix.append(linkColumnName(linkDef, objID));
          return shardPrefix.toString();
      }
docs: Return the row key for the Terms record that represents a link shard record for the
  given link, owned by the given object ID, referencing target objects in the given
  shard. The key format is:
  <pre>
  {shard number}/{link name}/{object ID}
  </pre>
  
  @param linkDef       {@link FieldDefinition} of a sharded link.
  @param objID         ID of object that owns link field.
  @param shardNumber   Shard number in the link's extent table.
  @return