Add empty_quantized (#18960)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18960
empty_affine_quantized creates an empty affine quantized Tensor from scratch.
We might need this when we implement quantized operators.
Differential Revision: D14810261
fbshipit-source-id: f07d8bf89822d02a202ee81c78a17aa4b3e571cc
