[ONNX] Improve error message for parse_arg in symbolic functions (#50512) (#51516)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51516
previous error message looks like this
```
RuntimeError: Unexpected node type: onnx::Gather
```
now
```
RuntimeError: Expected node type 'onnx::Constant' for argument 'groups' of node 'conv1d', got 'onnx::Gather'.
```
Repro example:
```python
torch.jit.script
def conv(x, w):
return F.conv1d(x, w, groups=x.shape[0])
class Net(nn.Module):
def forward(self, x, w):
return conv(x, w)
model = Net()
x = torch.randn(8, 8, 512)
w = torch.randn(8, 1, 3)
torch.onnx.export(model,
(x, w),
"file.onnx",
opset_version=12)
```
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26203118
Pulled By: SplitInfinity
fbshipit-source-id: 607b22f4cba4baa24154f197914b6817449ab9f8
