NOTE: This is just for testing. I am in the future going to add support for
serializing/handling actor instances. I messed with the serialization but I
found that b/c ActorInstances can take exprs and we generally do not serialize
exprs, we can't do this naively.
NOTE: We only do this for SIL parsed global actors so we do not have to update
code generated by SILGen. I want to do that at some point but a little later.