[Onnxifi] Support running with quantized int8 inputs (#41820)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41820
Pull Request resolved: https://github.com/pytorch/glow/pull/4721
In order to support int8 quantized tensor as an input to OnnxifiOp, we need to
- Add support to recognize and extract shape meta from int8 tensor at input of OnnxifiOp
- Make a copy of the input data and shift by 128 in Glow if input data is uint8 quantized tensor to get correct result because Glow uses int8 to represent the quantized data regardless.
- Propagate correct quantization parameters to through shape info in C2.
This diff implements the above.
Test Plan:
```
buck test caffe2/caffe2/contrib/fakelowp/test:test_int8_quantnnpi
```
Reviewed By: jackm321
Differential Revision: D22650584
fbshipit-source-id: 5e867f7ec7ce98bb066ec4128ceb7cad321b3392
