[Quant][fx][bc-breaking] Make convert.py smaller (#90189)
Summary: This commit moves helper functions that are not core
to the convert logic out of convert.py, which was more than
1000 lines. This helps with readability since a new developer
won't have to scroll through hundreds of lines of util functions
to understand the core logic. There should be no change in
functionality in this commit.
BC-breaking notes: The following helper functions that were
previously exposed under the `torch.ao.quantization.fx.convert`
namespace are now made private. Many of these are moved to the
new convert_utils.py
```
convert_custom_module
convert_standalone_module
convert_weighted_module
get_module_path_and_prefix,
has_none_qconfig,
insert_dequantize_node,
is_conversion_supported,
maybe_recursive_remove_dequantize,
replace_observer_or_dequant_stub_with_dequantize_node,
restore_state,
run_weight_observers,
```
Test Plan:
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
Reviewers: jerryzh168, vkuzo
Subscribers: jerryzh168, vkuzo
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90189
Approved by: https://github.com/jerryzh168
