[TensorExpr] simplify trivial adds/subs/muls even in Float (#37960)
Summary:
The IR Simplifier early exits when working with dtypes that are not safe to reorder. There are some cases where we still want to simplify ops in these dtypes: x + 0, x - 0, x * 0 and x * 1. It's safe to eliminate the op here and it reduces clutter in the expr.
Also added a quick simplification of casts which do nothing (their type is the same as the underlying).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37960
Differential Revision: D21457736
Pulled By: nickgg
fbshipit-source-id: 40e20a3b55fc1afb2ec50071812238a08bded2ac
