[torchlib] Update linear implementation to support 1d weights (#2340)

It is possible when users call `F.linear()` directly in PyTorch.

Author: justinchuby

onnxscript/function_libs/torch_lib/ops/nn.py

@@ -825,10 +825,15 @@ def aten_leaky_relu_backward(
 def aten_linear(input: TFloat, weight: TFloat, bias: Optional[TFloat] = None) -> TFloat:
     """linear(Tensor input, Tensor weight, Tensor? bias=None) -> Tensor"""
 
-    if len(input.shape) == 2:
+    if len(input.shape) == 2 and len(weight.shape) == 2:
         # Use Gemm for the rank 2 input
         return op.Gemm(input, weight, bias, transB=True)
-    weight_transposed = op.Transpose(weight, perm=[1, 0])
+    if len(weight.shape) == 1:
+        # In rare cases the weight can be 1d
+        weight_transposed = op.Unsqueeze(weight, [1])
+    else:
+        assert len(weight.shape) == 2
+        weight_transposed = op.Transpose(weight, perm=[1, 0])
     mul = op.MatMul(input, weight_transposed)
     if bias is None:
         return mul