Partially implement IConnectionPoint::connect()

This now works for direct connections, which is probably how most hosts
will use this.

src/common/logging/vst3.cpp

@@ -270,6 +270,15 @@ void Vst3Logger::log_request(bool is_host_vst,
     });
 }
 
+void Vst3Logger::log_request(bool is_host_vst,
+                             const YaConnectionPoint::Connect& request) {
+    log_request_base(is_host_vst, [&](auto& message) {
+        message << request.instance_id
+                << ": IConnectionPoint::connect(other = <IConnectionPoint* #"
+                << request.other_instance_id << ">)";
+    });
+}
+
 void Vst3Logger::log_request(
     bool is_host_vst,
     const YaEditController2::SetComponentState& request) {

src/common/logging/vst3.h

@@ -79,6 +79,7 @@ class Vst3Logger {
     void log_request(bool is_host_vst, const YaComponent::GetRoutingInfo&);
     void log_request(bool is_host_vst, const YaComponent::ActivateBus&);
     void log_request(bool is_host_vst, const YaComponent::SetActive&);
+    void log_request(bool is_host_vst, const YaConnectionPoint::Connect&);
     void log_request(bool is_host_vst,
                      const YaEditController2::SetComponentState&);
     void log_request(bool is_host_vst,

src/common/serialization/vst3.h

@@ -75,6 +75,7 @@ using ControlRequest = std::variant<Vst3PluginProxy::Construct,
                                     YaComponent::GetRoutingInfo,
                                     YaComponent::ActivateBus,
                                     YaComponent::SetActive,
+                                    YaConnectionPoint::Connect,
                                     YaEditController2::SetComponentState,
                                     YaEditController2::GetParameterCount,
                                     YaEditController2::GetParameterInfo,

src/common/serialization/vst3/plugin/connection-point.h

@@ -67,6 +67,29 @@ class YaConnectionPoint : public Steinberg::Vst::IConnectionPoint {
 
     inline bool supported() const { return arguments.supported; }
 
+    /**
+     * Message to pass through a call to
+     * `IConnectionPoint::connect(other_instance_id)` to the Wine plugin host.
+     */
+    struct Connect {
+        using Response = UniversalTResult;
+
+        native_size_t instance_id;
+
+        /**
+         * The other object this object should be connected to. When connecting
+         * two `Vst3PluginProxy` objects, we can directly connect the underlying
+         * objects on the Wine side.
+         */
+        native_size_t other_instance_id;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.value8b(instance_id);
+            s.value8b(other_instance_id);
+        }
+    };
+
     virtual tresult PLUGIN_API connect(IConnectionPoint* other) override = 0;
     virtual tresult PLUGIN_API disconnect(IConnectionPoint* other) override = 0;
     virtual tresult PLUGIN_API