layernorm: eager mode qat support (#39094)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39094
Adds eager mode QAT handling for LayerNorm
Test Plan:
```
python test/test_quantization.py TestQuantizationAwareTraining.test_normalization
```
Imported from OSS
Differential Revision: D21885260
fbshipit-source-id: 4f4c84a8bb8ba15dd78494f92569ed3a30d89169
