quantized layer norm: add to static quant (#36690)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36690
Adds the static quantization hook for LayerNorm
Test Plan:
```
python test/quantization/test_quantized_nn_mods.py ModuleAPITest.test_layer_norm
python test/quantization/test_quantization.py EagerModePostTrainingQuantTest.test_normalization
```
Imported from OSS
Differential Revision: D21055401
fbshipit-source-id: 188329f35359576d50ed0db5fb675ce68c28bf7d
