[ONNX] Update saved exported program in debugging report if the exporting passes run_decomposition() (#148617)

Previous to this PR, if the exporting passes run_decomposition(), the report still shows the exported_program before decomposition, which adds the difficulties to our users when they want to check the exported program that are used to translate to ONNX graph.

The following example is what we see before this PR:

```
# PyTorch ONNX Conversion Report

```
✅ Obtain model graph with `torch.export.export(..., strict=False)`
⚪ Obtain model graph with `torch.export.export(..., strict=True)`
⚪ Obtain model graph with `torch.jit.trace`
✅ Decompose operators for ONNX compatibility
❌ Translate the graph into ONNX
⚪ Run `onnx.checker` on the ONNX model
⚪ Execute the model with ONNX Runtime
⚪ Validate model output accuracy
```

## Error messages

```pytb

Traceback (most recent call last):

  File "/home/titaiwang/pytorch/torch/onnx/_internal/exporter/_core.py", line 707, in _translate_fx_graph
    _handle_call_function_node_with_lowering(

  File "/home/titaiwang/pytorch/torch/onnx/_internal/exporter/_core.py", line 486, in _handle_call_function_node_with_lowering
    raise _errors.DispatchError(

torch.onnx._internal.exporter._errors.DispatchError: No ONNX function found for <OpOverload(op='aten.slice', overload='Tensor')>. Failure message: No decompositions registered for the complex-valued input

The above exception was the direct cause of the following exception:

Traceback (most recent call last):

  File "/home/titaiwang/pytorch/torch/onnx/_internal/exporter/_core.py", line 1371, in export
    onnx_program = _exported_program_to_onnx_program(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  File "/home/titaiwang/pytorch/torch/onnx/_internal/exporter/_core.py", line 1007, in _exported_program_to_onnx_program
    values = _translate_fx_graph(
             ^^^^^^^^^^^^^^^^^^^^

  File "/home/titaiwang/pytorch/torch/onnx/_internal/exporter/_core.py", line 733, in _translate_fx_graph
    raise _errors.ConversionError(

torch.onnx._internal.exporter._errors.ConversionError: Error when translating node %slice_1 : [num_users=1] = call_function[target=torch.ops.aten.slice.Tensor](args = (%_to_copy, 0, 0, 9223372036854775807), kwargs = {}). See the stack trace for more information.

```

## Exported program

```python
ExportedProgram:
    class GraphModule(torch.nn.Module):
        def forward(self, x: "f32[3, 4]"):
             # File: /home/titaiwang/pytorch/test_slice_complex.py:6 in forward, code: x_complex = x.to(torch.complex64)
            to: "c64[3, 4]" = torch.ops.aten.to.dtype(x, torch.complex64);  x = None

             # File: /home/titaiwang/pytorch/test_slice_complex.py:8 in forward, code: return x_complex[:, :2]
            slice_1: "c64[3, 4]" = torch.ops.aten.slice.Tensor(to, 0, 0, 9223372036854775807);  to = None
            slice_2: "c64[3, 2]" = torch.ops.aten.slice.Tensor(slice_1, 1, 0, 2);  slice_1 = None
            return (slice_2,)

Graph signature: ExportGraphSignature(input_specs=[InputSpec(kind=<InputKind.USER_INPUT: 1>, arg=TensorArgument(name='x'), target=None, persistent=None)], output_specs=[OutputSpec(kind=<OutputKind.USER_OUTPUT: 1>, arg=TensorArgument(name='slice_2'), target=None)])
Range constraints: {}

```

## Analysis

PyTorch ONNX Conversion Analysis

## Model Information

The model has 0 parameters and 0 buffers (non-trainable parameters).
Number of parameters per dtype:
```python
defaultdict(<class 'int'>, {})
```
Number of buffers per dtype:
```python
defaultdict(<class 'int'>, {})
```

Inputs:
- `x`: `TensorMetadata(shape=torch.Size([3, 4]), dtype=torch.float32, requires_grad=False, stride=(4, 1), memory_format=torch.contiguous_format, is_quantized=False, qparams={})`

Outputs:
- `slice_2`: `TensorMetadata(shape=torch.Size([3, 2]), dtype=torch.complex64, requires_grad=False, stride=(4, 1), memory_format=None, is_quantized=False, qparams={})`

The FX graph has 5 nodes in total. Number of FX nodes per op:
- `placeholder`: 1
- `call_function`: 3
- `output`: 1

Of the call_function nodes, the counts of operators used are:

- `aten.slice.Tensor`: 2
- `aten.to.dtype`: 1

## ONNX Conversion Information

The model contains operators the dispatcher could not find registered ONNX decompositions for. This may be due to missing implementations, decompositions not registered correctly, or a bug in the dispatcher.

Errors grouped by operator:

- `aten.to.dtype`:     No decompositions registered for the real-valued input. Example node: `%to : [num_users=1] = call_function[target=torch.ops.aten.to.dtype](args = (%x, torch.complex64), kwargs = {})`. All nodes: `[to]`
- `aten.slice.Tensor`:     No decompositions registered for the complex-valued input. Example node: `%slice_1 : [num_users=1] = call_function[target=torch.ops.aten.slice.Tensor](args = (%to, 0, 0, 9223372036854775807), kwargs = {})`. All nodes: `[slice_1, slice_2]`

## Decomposition comparison

Ops exist only in the ExportedProgram before decomposition: `['aten.to.dtype']`

Ops exist only in the ExportedProgram after decomposition: `['aten._to_copy.default']`

```

Pull Request resolved: #148617
Approved by: https://github.com/justinchuby

Author: titaiwangms

torch/onnx/_internal/exporter/_core.py

@@ -1402,7 +1402,7 @@ def export(
                 _reporting.create_onnx_export_report(
                     report_path,
                     f"{_format_exceptions_for_all_strategies(failed_results)}\n\n{_format_exception(e)}",
-                    program,
+                    decomposed_program,
                     decomp_comparison=_reporting.format_decomp_comparison(
                         pre_decomp_unique_ops, post_decomp_unique_ops
                     ),