[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.

#184350 should give use the test coverage we need - remove the unit tests and regenerate known-never-zero.ll instead

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