Update base for Update on "[ExecuTorch] XNNPACK: prefer qc over qb when gs == k for non-int4"

* Prefer chanelwise over groupwise when possible for perf and for int8 which doesn't have groupwise support
* Fix bug / improve behavior for affine q/dq with gs == k for per_channel
* refactor is_per_channel_group state variable
* add QuantParams.__str__()

TODO - improve affine quant primitives - T237476295

Differential Revision: [D82060758](https://our.internmc.facebook.com/intern/diff/D82060758/)

**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D82060758/)!

[ghstack-poisoned]

Author: digantdesai