Revert to using weakref.rb, since it's based on a proper weak map. #4955
Opening as PR since this is a nontrivial change to put into 9.1, even though it aligns us better with MRI. Primary reason for this change is to get weakref specs to be more reliable...perhaps bringing our impl closer to theirs will do this.
This library used to use _id2ref (an internal API) for its
The new implementation of the library uses ObjectSpace::WeakMap,
This library used to use _id2ref (an internal API) for its implementation. This was not only very VM-specific (most VMs can't reconstitute an object reference given only its ID) but also buggy (an evacuated reference might get overlaid by a new object due to MRI's conservative GC and use of address for IDs. The new implementation of the library uses ObjectSpace::WeakMap, which is considered an internal API but which exposes an opaque weak identity map that can be implemented on other VMs more more easily. Given this and our need to continue descending from Delegate, moving back to the Ruby version may make sense.