[BE] Make Vec256 header only library (#50708)
Summary:
Do it by removing extraneous header dependencies.
None of the at::vec256 primitive depend on notion of Tensor, therefore none of the headers that vec256 depends on should include <ATen/Tensor.h>
Implicity test it be removing c10 and tensor dependency when building `vec256_test_all_types`
Split affine_quantizer into affine_quantizer_base (that contains methods operating on raw types) and affine_quantizer (which contains Tensor specific methods)
Fixes https://github.com/pytorch/pytorch/issues/50567
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50708
Reviewed By: walterddr
Differential Revision: D25949168
Pulled By: malfet
fbshipit-source-id: c3323be7252865a52c7d94026a5a39b494e44efb
