[xnnpack] Improve qd8-f16 testing

* Added a few qd8 fp16 tests for qc4w and qc8w
* Cleaned up and split fp16 and fp32 for basic tests to avoid getting confused regarding atol issues
* Created a TODO to look into atol values

Differential Revision: [D68350952](https://our.internmc.facebook.com/intern/diff/D68350952/)

[ghstack-poisoned]

Author: digantdesai