basic implementation of performing an init of the id after an assign of the actorSystem.

The resignID call within the initializer moved into DI, because an assignment to
the actorSystem, and thus initialization of the id, is no longer guaranteed to happen.
Thus, while we previously could model the resignation as a clean-up emitted on all
unwind paths in an initializer, now it's conditional, based on whether the id was
initialized. This is exactly what DI is designed to do, so we inject the resignation
call just before we call the identity's deinit.

lib/Sema/CodeSynthesisDistributedActor.cpp

@@ -76,6 +76,10 @@ static VarDecl *addImplicitDistributedActorIDProperty(
   // mark as nonisolated, allowing access to it from everywhere
   propDecl->getAttrs().add(
       new (C) NonisolatedAttr(/*IsImplicit=*/true));
+  // mark as @_compilerInitialized, since we synthesize the initializing
+  // assignment during SILGen.
+  propDecl->getAttrs().add(
+      new (C) CompilerInitializedAttr(/*IsImplicit=*/true));
 
   nominal->addMember(propDecl);
   nominal->addMember(pbDecl);