Generalised support for custom user layout changes
For IHP IO cells custom layout changes had to be made. In b9d9009e a callback was added that allows to do custom layout manipulation when the layout of a primitive is generated. Previously in 0830ff30 also a callback was added to do the same when creating a new cell in a library.
Both were marked as unstable API and this issue is for the finalization of the API implementing this feature.