Add a SetInspectedObject call that tells us which Core::Object a remote
client is currently looking it. Objects get notified when they gain
their first inspector, and when they lose their last one.
Since the returned object is now owned by the callee object, we can
simply vend a ChildType&. This allows us to use "." instead of "->"
at the call site, which is quite nice. :^)
Consider the old pattern for creating a Core::Object parent and child:
auto parent = Core::Object::construct(...);
auto child = Core::Object::construct(..., parent);
The above was an artifact of the pre-reference-counting Object era.
Now that objects have less esoteric lifetime management, we can replace
the old pattern with something more expressive:
auto parent = Core::Object::construct(...);
auto child = parent->add<Core::Object>(...);
This reads a lot more naturally, and it also means we can get rid of
all the parent pointer arguments to Core::Object subclass constructors.
