Adopting a reactive array or object

[wycats]

Currently, reactive.object and reactive.array copy the object's contents and freeze it to prevent further access.

In some situations, such as internal code loading data from a JSON endpoint that immediately wraps it in a "store", it would be better to "adopt" the JSON object. This would mean that we would turn the object itself into the proxy's target, and rely on the user not to access it directly anymore.

We could probably freeze the original object in development mode to help catch bugs, but this feels like a reasonable low-level primitive for people building abstractions around Starbeam.

[NullVoxPopuli]

@wycats is this dealt with?