[llvm] [ADT][NFC] Use isEqual for ImmutableSet/Map tree canonicalization (PR #207596)

[Balázs Benics via llvm-commits]

steakhal wrote:

> It looks like that this patch gives the performance benefit of node reclamation in a clean way. Is there a reason why node reclamation should not be removed at this point?

I think the same applies as always, for any default config:
We need motivation (this is pretty clear), an RFC, lastly a wide scale impact analysis: runtime cost (avg, median, p99, max) for memory, time footprint.

https://github.com/llvm/llvm-project/pull/207596