[quant][fx] Change prepare_fx and convert_fx to preserve the GraphModule type of input (#94412)
Summary:
Previously prepare_fx returns an ObservedGraphModule and convert_fx returns a QuantizedGraphModule,
this is to preserve the attributes since torch.fx.GraphModule did not preserve them, after https://github.com/pytorch/pytorch/pull/92062
we are preserving `model.meta`, so we can store the attributes in model.meta now to preserve them.
With this, we don't need to create a new type of GraphModule in these functions and can use GraphModule directly, this
is useful for quantization in pytorch 2.0 flow, if other transformations are using GraphModule as well, the quantization passes will be composable with them
Test Plan:
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
python test/test_quantization.py TestQuantizeFxModels
python test/test_quantization.py TestQuantizePT2E
Imported from OSS
Differential Revision: D42979722
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94412
Approved by: https://github.com/vkuzo
