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

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > Please can you merge with trunk latest and regenerate one more time
> 
> I merged with main and ran `update_checks` but the checks didn't change this time. Is that intended?

use the update_llc_test_checks.py script and ensure your newly compiled llc is in the path:
```
update_llc_test_checks.py --llc-binary=<path_to_latest_llc> known-never-zero.ll
```

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