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

[Matt Arsenault via llvm-commits]

arsenm 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? 

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