Require virtual object selves to be declared Far

[FUDCo]

Fixes bug #3562

[erights]

What about a negative test, where the new assert is violated?

[warner]

BTW I think it's accurate to say "Representatives are Far" rather than trying to define a "virtual object self": We use Representative and Presence and Remotable to refer to the three concrete JS Objects that userspace code interacts with. The "virtual object" is the abstract object with state and behavior, which has a longer lifetime than any single ephemeral+concrete Representative.

At least, that's the terminology that I use (and that I think we need) from everywhere except the interior of the virtual object manager. I guess I'm thinking the initialRepresentative variable is slightly misnamed: the user-provided "kind constructor" returns a record with two pieces (an init function for making new virtual objects, and a self behavior record which becomes the actual concrete Representative Object), but the overall record is being stored in initialRepresentative

[warner]

In addition to @erights 's recommended negative test, please also update docs/virtual-objects.md to include the Far requirement.

Apart from that the code changes look great.

[erights]

LGTM