[llvm] [DAG] Fold trunc(avg(x, y)) for avgceil/floor u/s nodes if they have sufficient leading zero/sign bits (PR #152273)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon approved this pull request.

LGTM - cheers

https://github.com/llvm/llvm-project/pull/152273