Use the std::derived_from concept when applicable

This probably makes things much clearer at a glance instead of using a
blanked typename.

src/common/communication/vst2.h

@@ -152,8 +152,8 @@ class Vst2EventHandler : public AdHocSocketHandler<Thread> {
      * @relates Vst2EventHandler::receive_events
      * @relates passthrough_event
      */
-    template <typename D>
-    intptr_t send_event(D& data_converter,
+    template <std::derived_from<DefaultDataConverter> Converter>
+    intptr_t send_event(Converter& data_converter,
                         std::optional<std::pair<Vst2Logger&, bool>> logging,
                         int opcode,
                         int index,

src/plugin/bridges/vst2.cpp

@@ -183,7 +183,7 @@ Vst2PluginBridge::~Vst2PluginBridge() noexcept {
     }
 }
 
-class DispatchDataConverter : DefaultDataConverter {
+class DispatchDataConverter : public DefaultDataConverter {
    public:
     DispatchDataConverter(std::vector<uint8_t>& chunk_data,
                           AEffect& plugin,

src/wine-host/bridges/vst2.cpp

@@ -486,7 +486,7 @@ intptr_t Vst2Bridge::dispatch_wrapper(AEffect* plugin,
     }
 }
 
-class HostCallbackDataConverter : DefaultDataConverter {
+class HostCallbackDataConverter : public DefaultDataConverter {
    public:
     HostCallbackDataConverter(AEffect* plugin,
                               VstTimeInfo& last_time_info) noexcept