[llvm] [mlir] [MLIR][Python] reland (narrower) type stub generation (PR #157930)

[Maksim Levental via llvm-commits]

makslevental wrote:

> My understanding is that `PyRegionList`

Err sorry I lost track of the context. Yes your explanation makes sense. So then we should just add a generic type hint to sliceable? That CRTP already captures the name of the instantiating class.

https://github.com/llvm/llvm-project/pull/157930