don't call floor for symint unless necessary (#94365)
Per @ezyang's advice, added magic sym_int method. This works for 1.0 * s0 optimization, but can't evaluate `a>0` for some args, and still misses some optimization that model rewrite achieves, so swin still fails
(rewrite replaces `B = int(windows.shape[0] / (H * W / window_size / window_size))` with `B = (windows.shape[0] // int(H * W / window_size / window_size))` and model passes)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94365
Approved by: https://github.com/ezyang
