Add folder for torch.aten.Int.Tensor

This is to fold the common pattern from Bert inference like:
```
%111 = torch.prim.NumToTensor.Scalar %110 : !torch.int ->
    !torch.vtensor<[],si64>
%112 = torch.aten.Int.Tensor %111 : !torch.vtensor<[],si64> ->
    !torch.int
```

include/torch-mlir/Dialect/Torch/IR/GeneratedAtenOps.td

@@ -2197,6 +2197,7 @@ def Torch_AtenIntTensorOp : Torch_Op<"aten.Int.Tensor", [
     Torch_IntType:$result
   );
   let assemblyFormat = "$a attr-dict `:` type($a) `->` type($result)";
+  let hasFolder = 1;
 }
 
 def Torch_AtenDropoutOp : Torch_Op<"aten.dropout", [

lib/Dialect/Torch/IR/TorchOps.cpp

@@ -1076,5 +1076,14 @@ OpFoldResult PrimDtypeOp::fold(ArrayRef<Attribute> operands) {
   }
   return nullptr;
 }
+
+OpFoldResult AtenIntTensorOp::fold(ArrayRef<Attribute> operands) {
+  // If an scalar number is converted to a 0-d tensor and passed on to
+  // aten.Int.Tensor, fold to the scalar number.
+  if (auto numToTensorScalar = a().getDefiningOp<PrimNumToTensorScalarOp>())
+    return numToTensorScalar.a();
+  return nullptr;
+}
+
 #define GET_OP_CLASSES
 #include "torch-mlir/Dialect/Torch/IR/TorchOps.cpp.inc"

python/torch_mlir/dialects/torch/importer/jit_ir/build_tools/torch_ods_gen.py

@@ -568,7 +568,7 @@ def emit_aten_ops(torch_ir_dir: str, registry: Registry):
         emit("aten::gather : (Tensor, int, Tensor, bool) -> (Tensor)")
         emit("aten::IntImplicit : (Tensor) -> (int)")
         emit("aten::tensor.float : (float, int?, Device?, bool) -> (Tensor)")
-        emit("aten::Int.Tensor : (Tensor) -> (int)")
+        emit("aten::Int.Tensor : (Tensor) -> (int)", has_folder=True)
         emit("aten::dropout : (Tensor, float, bool) -> (Tensor)")
 
         # Dict ops.

test/Dialect/Torch/canonicalize.mlir

@@ -594,3 +594,14 @@ func @torch.prim.TupleIndex$out_of_bound(%t0: !torch.tensor, %t1: !torch.tensor,
     %1 = torch.prim.TupleIndex %0, %int3 : !torch.tuple<!torch.tensor, !torch.tensor, !torch.tensor>, !torch.int -> !torch.tensor
     return %1 : !torch.tensor
 }
+
+
+// CHECK-LABEL:   func @torch.aten.Int.Tensor(
+// CHECK-SAME:            %[[NUM:.*]]: !torch.int) -> !torch.int {
+// CHECK:           %[[T:.*]] = torch.prim.NumToTensor.Scalar %[[NUM]] : !torch.int -> !torch.vtensor<[],si64>
+// CHECK:           return %[[NUM]] : !torch.int
+func @torch.aten.Int.Tensor(%arg0: !torch.int) -> !torch.int {
+  %tensor = torch.prim.NumToTensor.Scalar %arg0: !torch.int -> !torch.vtensor<[],si64>
+  %scalar = torch.aten.Int.Tensor %tensor : !torch.vtensor<[],si64> -> !torch.int
+  return %scalar : !torch.int
+}