Move sym_int and sym_float alongside SymInt / SymFloat in base torch package (#91317)
This PR moves the definitions for:
* `sym_int`
* `sym_ceil` (used only for `sym_int`)
* `sym_floor` (used only for `sym_int`)
* `sym_float`
from `torch/fx/experimental/symbolic_shapes.py` to `torch/__init__.py`, where `SymInt` and `SymFloat` are already defined.
This removes the need for several in-line imports, and enables proper JIT script gating for #91318. I'm very open to doing this in a better way!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91317
Approved by: https://github.com/ezyang, https://github.com/anijain2305
