quantized conv: add support for graph mode BC testing, and increase coverage (#43524)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43524
1. adds support for testing BC on data format and numerics for graph mode
quantized modules
2. using the above, adds coverage for quantized conv2d on graph mode
Test Plan:
```
python test/test_quantization.py TestSerialization.test_conv2d_nobias
python test/test_quantization.py TestSerialization.test_conv2d_graph
python test/test_quantization.py TestSerialization.test_conv2d_nobias_graph
```
Imported from OSS
Reviewed By: supriyar
Differential Revision: D23335222
fbshipit-source-id: 0c9e93a940bbf6c676c2576eb62fcc725247588b
