[clang] [llvm] [IR] Change representation of getelementptr inrange (PR #84341)

[Arthur Eubanks via cfe-commits]

aeubanks wrote:

the only use of this is GlobalSplit, and it cares about ranges relative to the GlobalVariable, so if we're not planning on using this in more cases then I'd say relative to the source pointer makes sense.

not sure if inrange would ever be useful for more than GlobalSplit, like being able to tighten the possible values of a load from a const array if we know the load is in some small range of the array, which doesn't seem super useful

https://github.com/llvm/llvm-project/pull/84341