[llvm] [DAGCombine] Propagate truncate to operands (PR #98666)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

@RKSimon, thanks for the ping on this. Some other work items came up, and I couldn't give this PR the attention it needed. 

It should now be ready for another round of review :) 

https://github.com/llvm/llvm-project/pull/98666