[llvm] [DAG] isKnownNeverZero - add ISD::SHL DemandedElts handling and tests (PR #183772)

[via llvm-commits]

Joeljm1 wrote:

Thank you so much for your help @RKSimon . This was my first opensource contribution and you were very helpful

https://github.com/llvm/llvm-project/pull/183772