Move WantsConfiguration to common

We'll also need this for CLAP.

src/common/serialization/common.h

@@ -22,6 +22,7 @@
 #include <cstdint>
 #include <type_traits>
 
+#include "../configuration.h"
 #include "../plugins.h"
 
 // The plugin should always be compiled to a 64-bit version, but the host
@@ -43,6 +44,23 @@ struct Ack {
     void serialize(S&) {}
 };
 
+/**
+ * Marker struct to indicate the other side (the plugin) should send a copy of
+ * the configuration. During this process we will also transmit the version
+ * string from the host, so we can show a little warning when the user forgot to
+ * rerun `yabridgectl sync` (and the initialization was still successful).
+ */
+struct WantsConfiguration {
+    using Response = Configuration;
+
+    std::string host_version;
+
+    template <typename S>
+    void serialize(S& s) {
+        s.text1b(host_version, 128);
+    }
+};
+
 /**
  * An object containing the startup options for hosting a plugin. These options
  * are passed to `yabridge-host.exe` as command line arguments, and they are