Build a performance test suite for WaitingOnGraph

https://github.com/llvm/llvm-project/issues/179611 reported a serious performance regression from LLVM 21 to LLVM 22 that was largely caused by `WaitingOnGraph`s dependence propagation algorithm.

Now that `WaitingOnGraph` is a standalone data structure we should try to build some performance reporting / testing infrastructure around it so that we can spot performance regressions like this earlier next time.

I think we could extend WaitingOnGraph with an option to dump the inputs to its simplify and emit operations, and build tooling to replay these operations either in a regression test tool or a unit test. We should use this to put together a performance suite. Ideally one that would allow automated detection of regressions.