[GH-12209] Prototype for loading partial objects fully

[beberlei]

A partial object is actually just a proxy with more than just the ID field pre-populated. If we access a property of the partial object that is not already loaded, then we can trigger the proxy to load the missing fields.

Problems:

• Embedded Objects need to be created as lazy ghosts as well that trigger lazy loading of the parent.
• Changesets are overwritten by the proxy load.