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

[Nikita Popov via llvm-commits]

nikic wrote:

Compile-time is indeed mildly positive: http://llvm-compile-time-tracker.com/compare.php?from=769952d72ff383e0e5fda46802fb8717712784d3&to=0df283c8117daebd019927aff76f78f43cfb5569&stat=instructions%3Au

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