[llvm] [DAG] isKnownNeverZero - add ISD::UDIV/SDIV DemandedElts handling and tests (PR #183227)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

Take a look at #183934 - I had to add a vector store to prevent scalarisation

https://github.com/llvm/llvm-project/pull/183227