GH-96068: Document object layout

[markshannon]

• Issue: Document object layout, particularly the managed dictionary. #96068

[Fidget-Spinner]

Should we place this in the devguide instead?

[markshannon]

Maybe, but the further the docs are separated from the code, the more likely there are to get out of sync.

Ideally, they would be in the same file and automatically extracted. https://en.wikipedia.org/wiki/Literate_programming

[ericsnowcurrently]

Maybe, but the further the docs are separated from the code, the more likely there are to get out of sync.

Agreed. I expect the object layout to be unstable enough that keeping it with the code will be important. Such implementation documentation in the devguide is more appropriate for designs that don't change much.

That said, it would be worth having a link in the devguide pointing to Objects/object_layout.md.

[markshannon]

#96209