Add ToString() to Modules

Add ToString() to Module and classes inherit Module to help debug.

Bug: 144304945

Test: cert
Change-Id: I8535c6ddb182fd26a7c62b30679cfb90a5168ebe
diff --git a/gd/module.h b/gd/module.h
index 88bc528..045865d 100644
--- a/gd/module.h
+++ b/gd/module.h
@@ -19,6 +19,7 @@
 #include <functional>
 #include <future>
 #include <map>
+#include <string>
 #include <vector>
 
 #include "common/bind.h"
@@ -75,6 +76,8 @@
   // Release all resources, you're about to be deleted
   virtual void Stop() = 0;
 
+  virtual std::string ToString() const;
+
   ::bluetooth::os::Handler* GetHandler() const;
 
   const ModuleRegistry* GetModuleRegistry() const;