Allow the module to be properly unloaded

Terminating the host process will cause all sockets to be closed so we
can join the threads.

src/plugin/bridges/vst3.h

@@ -55,6 +55,12 @@ class Vst3PluginBridge : PluginBridge<Vst3Sockets<std::jthread>> {
      */
     Vst3PluginBridge();
 
+    /**
+     * Terminate the Wine plugin host process and drop all work when the module
+     * gets unloaded.
+     */
+    ~Vst3PluginBridge();
+
     /**
      * When the host loads the module it will call `GetPluginFactory()` which
      * will in turn call this function. The idea is that we return an