Implement IComponent::getState()

With this the basic IComponent interface is fully implemented. Next will
be `IAudioProcessor` and `IConnectionPoint` as additions to IComponent.
We'll use the same `known_iids` mechanism as used in the plugin factory.

src/common/serialization/vst3.h

@@ -68,6 +68,7 @@ using ControlRequest = std::variant<YaComponent::Construct,
                                     YaComponent::ActivateBus,
                                     YaComponent::SetActive,
                                     YaComponent::SetState,
+                                    YaComponent::GetState,
                                     YaPluginFactory::Construct,
                                     YaPluginFactory::SetHostContext>;