dbr quant: refactor `get_func_output_obs_type` to only use `seen_op_info` (#68341)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68341
Before this PR, `get_func_output_obs_type` used information from the
incoming op and its arguments, which makes it hard to cache.
This PR refactors `get_func_output_obs_type` to only use information
collected during tracing. This will make it easier to make performance
improvements in a future PR.
Test Plan:
```
python test/test_quantization.py TestQuantizeDBR
```
Reviewed By: jerryzh168
Differential Revision: D32463755
Pulled By: vkuzo
fbshipit-source-id: 25a220de652f0285685d43aedf7392082104b26c
