[quant] change observer FQNs generated in prepare step (#65420)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65420
Context: In some FB use cases we have a need to map observer stats from train model checkpoint to inference model. We observerd that some buffer names are different becuase the intermediate activation tensors
are generated differently across train and inference model. More details in https://fb.quip.com/PtGcAR0S5CQP
Currently, for each observer (activation_post_process), the FQN of the module inserted is determined based on the FQN of the input tensor it is observing.
In this change we change the observer FQN to include the FQN of the op/module it is observing rather than tensor/intermediate op names along with the “input”/“output” detail.
Before
```
def forward(self, x):
x_activation_post_process_0 = self.x_activation_post_process_0(x); x = None
mods1_w = self.mods1.w
mods1_w_activation_post_process_0 = self.mods1_w_activation_post_process_0(mods1_w); mods1_w = None
mods1_b = self.mods1.b
linear = torch.nn.functional.linear(x_activation_post_process_0, mods1_w_activation_post_process_0, bias = mods1_b); x_activation_post_process_0 = mods1_w_activation_post_process_0 = mods1_b = None
linear_activation_post_process_0 = self.linear_activation_post_process_0(linear); linear = None
return linear_activation_post_process_0
```
After
```
def forward(self, x):
mods1_input_activation_post_process_0 = self.mods1_input_activation_post_process_0(x); x = None
mods1_w = self.mods1.w
mods1_w_activation_post_process_0 = self.mods1_w_activation_post_process_0(mods1_w); mods1_w = None
mods1_b = self.mods1.b
linear = torch.nn.functional.linear(mods1_input_activation_post_process_0, mods1_w_activation_post_process_0, bias = mods1_b); x_activation_post_process_0 = mods1_w_activation_post_process_0 = mods1_b = None
mods1_output_activation_post_process_0 = self.mods1_output_activation_post_process_0(linear); linear = None
return mods1_output_activation_post_process_0
```
Test Plan:
python test/test_quantization.py test_observer_fqn
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D31088652
fbshipit-source-id: 2f1526f578a13000b34cfd30d11f16f402fd3447
