Once rich errors are out, I think `accumulating` s...

# arrow-contributors

[Youssef Shoaib [MOD]]

Once rich errors are out, I think accumulating should move to them. RaiseAccumulate.Error is a perfect candidate to be an error class (it has no generics, and is literally named Error lol).
I'm not 100% sure on the feasibility of preserving binary compatibility here, but I think it can be done with a few `@JvmName`s and some elbow grease