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

[via llvm-commits]

AtariDreams wrote:

@llvmbot request to cherry-pick this into release (and only this, plus the test case commit too I suppose).

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