[quant][fx] add pass to duplicate dequant nodes with multi use (#67118)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67118
Fixes a bug in the reference pattern support for nn.Linear when the same quantized input is shared across multiple Linear nodes.
This PR adds a pass to duplicate the dequant nodes for each use so that for a case like
```
x -> quant -> dequant -> linear1 - quant1
|
linear2 - quant2
```
We duplicate the dequant nodes
```
x -> quant -> dequant1 -> linear1 - quant1
|
dequant2-> linear2 - quant2
```
So that we can match each pattern in the loweing step
We also add a pass to remove the extra/duplicate dequant nodes that may be leftover from the above pass if we don't lower them based on pattern match
Test Plan:
python test/test_quantization.py test_ref_pattern_multi_use
Imported from OSS
Reviewed By: mrshenli
Differential Revision: D31873511
fbshipit-source-id: aea0819222f084635157426743a50e065e6503c3
