Change SymIntNode into an intrusive pointer (#82432)
This will make the pointer type a single word, which is important
for packing it into an int64_t
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82432
Approved by: https://github.com/albanD, https://github.com/Krovatkin
