[llvm] [InstCombine] Canonicalize `(sitofp x)` -> `(uitofp x)` if `x >= 0` (PR #82404)

[via llvm-commits]

goldsteinn wrote:

> define float @src(i32 %shr.i) {
>   %and.i = and i32 %shr.i, 32767
>   %sub = uitofp i32 %and.i to float
>   %add = fadd float %sub, -16383.0
>   ret float %add
> }

See: https://github.com/llvm/llvm-project/pull/84389

https://github.com/llvm/llvm-project/pull/82404