[ao] making _is_activation_post_process private (#87520)
Summary: same function in observer and quantize, consolidated to a
single function. Note the definitions were slightly different, I've
changed the definition to be maximally inclusive so that the name of the
function is more accurate
Test Plan: python test/test_public_bindings.py
python test/test_quantization.py
Reviewers:
Subscribers:
Tasks:
Tags:
Differential Revision: [D40709276](https://our.internmc.facebook.com/intern/diff/D40709276)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87520
Approved by: https://github.com/jcaip
