Add the Factorization Machine Layer / Operator.

[lcy-seso]

Factorization machines can be compared to support vector machines (SVMs) with a polynomial kernel, which is highly used in recommendation problem to estimate more complex interactions (2-order or even higher).

FM helps to make learning interactions among large-scale categorical features tractable.

[typhoonzero]

Shall we add as a Layer or an Operator?

[lcy-seso]

I prefer to add a layer first, so we can use it under the current framework. And then port it to an operator under the new framework.