Redesign how interface instantiation works

Transferring some argument pack is much easier than trying to
deserialize into an existing object when you also have to transfer more
information than just that object.

src/common/serialization/vst3/README.md

@@ -3,6 +3,12 @@
 TODO: Once this is more fleshed out, move this document to `docs/`, and perhaps
 replace this readme with a link to that document.
 
+TODO: There are now two approaches in use: the factory takes an interface
+pointer for serialization and deserializes into an object directly, and the
+component uses an args struct because the alternative involving pointers is just
+too unsafe (as we also have to communicate additional payload data). This should
+probably be unified into only using the latter appraoch.
+
 The VST3 SDK uses an architecture where every object inherits from an interface,
 and every interface inherits from `FUnknown` which offers a dynamic casting
 interface through `queryInterface()`. Every interface gets a unique identifier.