Refactor event receiving to optimize MIDI handlign

This keeps compatibility with some weirdly designed plugins (such as
Kontakt) while avoiding some unnecessary data transformations. Before
this we'd convert from a `DynamicVstEvents` object to a `VstEvents`
object, back to a `DynamicVstEvents` and then finally back into another
`VstEvents` object. With this change we can skip the second half of the
conversions.

src/plugin/host-bridge.cpp

@@ -172,9 +172,9 @@ HostBridge::HostBridge(audioMasterCallback host_callback)
     host_callback_handler = std::thread([&]() {
         try {
             while (true) {
-                passthrough_event(vst_host_callback,
-                                  std::pair<Logger&, bool>(logger, false),
-                                  &plugin, host_callback_function);
+                receive_event(
+                    vst_host_callback, std::pair<Logger&, bool>(logger, false),
+                    passthrough_event(&plugin, host_callback_function));
             }
         } catch (const boost::system::system_error&) {
             // This happens when the sockets got closed because the plugin