Moved functions to pytorch_utils.py (#16625)

* Moved functions to pytorch_utils.py

* isort formatting

* Reverted tf changes

* isort, make fix-copies

* documentation fix

* Fixed Conv1D import

* Reverted research examples file

* backward compatibility for pytorch_utils

* missing import

* isort fix

docs/source/en/internal/modeling_utils.mdx

@@ -19,7 +19,7 @@ Most of those are only useful if you are studying the code of the models in the
 
 ## Pytorch custom modules
 
-[[autodoc]] modeling_utils.Conv1D
+[[autodoc]] pytorch_utils.Conv1D
 
 [[autodoc]] modeling_utils.PoolerStartLogits
     - forward
@@ -40,15 +40,15 @@ Most of those are only useful if you are studying the code of the models in the
 
 ## PyTorch Helper Functions
 
-[[autodoc]] apply_chunking_to_forward
+[[autodoc]] pytorch_utils.apply_chunking_to_forward
 
-[[autodoc]] modeling_utils.find_pruneable_heads_and_indices
+[[autodoc]] pytorch_utils.find_pruneable_heads_and_indices
 
-[[autodoc]] modeling_utils.prune_layer
+[[autodoc]] pytorch_utils.prune_layer
 
-[[autodoc]] modeling_utils.prune_conv1d_layer
+[[autodoc]] pytorch_utils.prune_conv1d_layer
 
-[[autodoc]] modeling_utils.prune_linear_layer
+[[autodoc]] pytorch_utils.prune_linear_layer
 
 ## TensorFlow custom layers