[IndVarSimplify] Don't replace IV user with unsafe loop-invariant (PR45360)

[IndVarSimplify] Don't replace IV user with unsafe loop-invariant (PR45360)

Summary:
As [[ https://bugs.llvm.org/show_bug.cgi?id=45360 | PR45360 ]] reports,
with new cost-model we can sometimes end up being able to expand `udiv`/`urem` instructions.
And that exposes at least one instance of when we do that
regardless of whether or not it is safe to do.
In this particular case, it's `SimplifyIndvar::replaceIVUserWithLoopInvariant()`.

It seems to me, we simply need to check with `isSafeToExpandAt()` first.

The test isn't great. I'm not sure how to make it only run `-indvars`.

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=45360 | PR45360 ]].

Reviewers: mkazantsev, reames, helloqirun

Reviewed By: mkazantsev

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82108