[MergeFunc] Handle ConstantRange attributes (#88584)

It is possible to update
[AttributeImpl::operator<](https://github.com/andjo403/llvm-project/blob/a9da350aadfb5c86d36ae18398471558b22c1309/llvm/lib/IR/Attributes.cpp#L744)
instead but feels strange to say that a range is less then an other
range.