[PT2E][Quant] Refactor quantizer and qnnpack qantizer code to support dqlinear config (#99399)
This diff introduces a few refactors:
- Move observer creation to utils.py.
- Use quantization spec to supply args to observers.
- Use annotation function registration corresponding QuantizationConfig. This
will be later used in dynamic quantized linear.
Differential Revision: [D45073790](https://our.internmc.facebook.com/intern/diff/D45073790/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99399
Approved by: https://github.com/jerryzh168
