[llvm] ValueTracking: simplify udiv/urem recurrences (PR #108973)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> Can this code be integrated in the shift handling above? It seems pretty similar -- but not quite the same, and I'm suspicious of differences :)

The only difference is a smarter context. Given that the context is a little difficult to test, I've integrated the code at the cost of a worse context. We can try to improve the context in a follow-up, but I'm not sure what tests we can write.

https://github.com/llvm/llvm-project/pull/108973