[llvm] [ConstantRange] Fix off by 1 bugs in UIToFP and SIToFP handling. (PR #86041)

[via llvm-commits]

llvmbot wrote:

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Failed to cherry-pick: release/18.x

https://github.com/llvm/llvm-project/actions/runs/8378684757

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

https://github.com/llvm/llvm-project/pull/86041