Handle `Rational` divisors in `FloorDiv`. (#106644)
Follow-up: #101173
This PR fixes the bug presented in #101173 by creating a special case for `sympy.Rational`
divisors, inside `FloorDiv` evaluation. In summary:
```python
FloorDiv(a, Rational(1, b))
a * b
```
Besides that, this PR also does 2 other things:
- Replaces the use of the old `sympy.Mod` by the internal `Mod` (there were a few places
that were still looking for the SymPy one)
- Introduces debugging logs to the translation validator. These can be seen by setting the
environment variable: `TORCH_LOGS=+torch.fx.experimental.validator`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106644
Approved by: https://github.com/ezyang
ghstack dependencies: #106643
