message: Add bool support for unique_with_counts
  This fix tries to address the issue raised in 29863 where
  unique_with_counts does not support bool dtype yet.
  This fix fixes 29863.
diff: @@ -237,6 +237,7 @@ class UniqueOp : public OpKernel {
  UniqueOp<type, int64>)
  TF_CALL_REAL_NUMBER_TYPES(REGISTER_UNIQUE);
  REGISTER_UNIQUE(string)
  +REGISTER_UNIQUE(bool)
  #undef REGISTER_UNIQUE
  // Fake integer GPU kernels so that the use of Unique in optimizers (to
  