Preview changes in object signature in dev

For multi-version docs, we have many authoring possibilities for specifying what’s new in which versions in guide pages and other sections. We also plan to show upcoming features with section badges in such pages. (UPDATE: implemented in dev).

Taking this further, in the reference section, there may be API changes that users will want to know about in an upcoming version. For this type of situation, we should present a view of an upcoming state of the object signature (perhaps flagging specifically which parts are new, changed, or removed). This could be a great help for users of a library to be on top of API changes that affect their workflows.