SparseTensor multiplication in tf.keras.layers.Dense

[sfujiwara]

System information

• TensorFlow version (you are using): 1.12.0
• Are you willing to contribute it (Yes/No): Yes

Describe the feature and the current behavior/state.
In keras.layers.Dense, tf.sparse_tensor_dense_matmul is called for SparseTensor as this.
But in tf.keras, only tf.tensordot (which can not treats SparseTensor) is called as this.

Do you have any plan to treat SparseTensor in tf.keras?

Will this change the current api? How?
We can fix it simply using tf.sparse_tensor_dense_matmul.
If needed, I can create PR.

[ymodak]

I believe we have this feature now in TF tf.sparse.sparse_dense_matmul. Please reopen if that's not the case. Thanks!