[llvm] [ValueTracking] Consistently propagate `DemandedElts` in ValueTracking functions (PR #99080)

[via llvm-commits]

goldsteinn wrote:

> I don't think there were demanded elts arguments in the original implementations. Should only require an extractelement with a constant index on any test?

Correct, if there are any cases you think need the coverage I can add (all if necessary).

https://github.com/llvm/llvm-project/pull/99080