[quant][graphmode] Fold quantized prepacking ops (#35077)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35077
Fold the prepack ops: `quantized::linear_prepack` and `quantized::conv2d_prepack` after
`freeze`
Test Plan:
python test/test_jit.py
Imported from OSS
Differential Revision: D20655301
fbshipit-source-id: fbb4223323f788c88db7b55cfafda46fad106d49
