[quant] Refactor quantize clamping into float_to_apot util function (#80885)
### Summary:
This PR moves the clamping functionality from `quantize` to `float_to_apot` util function to align with the uniform quantize workflow in the codebase.
### Test Plan:
Run unit tests with:
python pytorch/test/quantization/core/experimental/test_quantizer.py
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80885
Approved by: https://github.com/dzdang
