[Executorch][XNNPACK] Quantized hardtanh (#97387)
Lower Quantized Hardtanh to XNNPACK
Also add symmetric quantization support for hardtanh in executorch backend config
Differential Revision: [D43901222](https://our.internmc.facebook.com/intern/diff/D43901222/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97387
Approved by: https://github.com/salilsdesai
