[Quant] lower fused LinearTanh for onednn backend (#89188)
**Summary**
Add fuser method and quantization mappings for `QLinearLeakyReLU` for int8 inference for onednn backend. The fusion and lowering are supported only in FX mode.
**Test plan**
python test_quantization.py TestFuseFx TestQuantizeFx
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89188
Approved by: https://github.com/jgong5, https://github.com/jerryzh168
