E2E SymInt example narrow_copy
This **roughly** corresponds to Goal 3.2 in https://docs.google.com/document/d/1iiLNwR5ohAsw_ymfnOpDsyF6L9RTUaHMpD8YLw-jxEw/edit#
Namely:
It adds the following:
* SymbolicIntNode interface
* LazySymbolicIntNode implementation
* Lazy `narrow_copy` implementation
* Need add support for SymInt in codegen
* Test (below)
```cpp
TEST(LazyDynamicOpsTest, NarrowCopy) {
auto x = torch::rand({5, 10, 10}).to(kLazy);
const size_t Y_DIM = 3;
const size_t X_DIM_INDEX = 2;
auto y = torch::rand({Y_DIM}).to(kLazy);
auto ly = torch::lazy::TryGetLtcTensor(y);
auto dim_node = MakeNode<SizeNode>(ly->GetIrValue(), 0);
auto lmn = new torch::lazy::SymbolicIntNode(dim_node);
auto z = x.narrow_copy(X_DIM_INDEX, 0, lmn->toSymInt());
AllClose(z.cpu(), x.cpu().narrow_copy(X_DIM_INDEX, 0, Y_DIM));
}
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75759
Approved by: https://github.com/wconstab
