[llvm] [DAG] Add freeze(assertext(x)) -> assertext(x) folds (PR #94491)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Something like the following:

```
declare void @g(i1 zeroext)
define void @f(float %f) {
  %i = fptoui float %f to i1
  call void @g(i1 zeroext %i)
  ret void
}
```

Targeting AArch64, we don't actually zero-extend the argument.  Which is a problem if it's instant UB.

https://github.com/llvm/llvm-project/pull/94491