[Quant] Add fused linear-tanh op for onednn backend (#88879)
**Summary**
Post op fusion can reduce data movement overhead and improve inference performance. This PR adds fused `linear-tanh` op for `onednn` backend, which will be used for int8 inference with `onednn` backend. Linear-tanh is found in models like CGAN.
Cannot call this op with other quantization backends otherwise an error is thrown.
**Test Plan**
python test_quantization.py TestQuantizedLinear
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88879
Approved by: https://github.com/jgong5, https://github.com/jerryzh168
