fx quant: fix crash on output dicts and lists (#58416)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58416
https://github.com/pytorch/pytorch/pull/57519 had a regression not
caught by CI, it added an assertion which failed on various model
output types.
This PR removes the assertion and adds the logic to observe graph
outputs in a way that supports arbitrary output formats.
Test Plan:
```
python test/test_quantization.py TestQuantizeFx.test_output_lists_and_dicts
```
Imported from OSS
Reviewed By: z-a-f
Differential Revision: D28479946
fbshipit-source-id: bcce301f98a057b134c0cd34ab0ca96ba457863f
