Add wrapper code to wrap an ET kernel into an ATen kernel (#2186)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2186

Add an API that is able to wrap ExecuTorch kernels into ATen kernels.

This can save kernel author time, if they start from ExecuTorch kernels.

In this PR we only support the following argument types to ExecuTorch
kernels:

* Tensor-like. `torch::executor::Tensor` and its reference/const
  reference.
* Primitive types. `int` `float` etc.

Doesn't support ArrayRef or Optional yet.

Reviewed By: lucylq

Differential Revision: D54394149

fbshipit-source-id: 8288d05f4948adbc4f14f96641438afa20a94765