[llvm] [ADT] Rewrite ImmutableSet/Map in-order iterator without per-node state (PR #205552)

[Gábor Horváth via llvm-commits]

Xazax-hun wrote:

Added a table with the benchmark results. Looks like multiple sources confirmed that this is really good for performance, so I am merging this for now. But please report back with any additional benchmarks and findings.

https://github.com/llvm/llvm-project/pull/205552