util: Document why ArgsManager (con/de)structor is not inline

src/util/settings.h

@@ -9,7 +9,7 @@
 #include <string>
 #include <vector>
 
-#include <univalue.h> // For util::SettingsValue = UniValue
+class UniValue;
 
 namespace util {
 

src/util/system.cpp

@@ -226,10 +226,11 @@ static bool CheckValid(const std::string& key, const util::SettingsValue& val, u
     return true;
 }
 
-ArgsManager::ArgsManager()
-{
-    // nothing to do
-}
+// Define default constructor and destructor that are not inline, so code instantiating this class doesn't need to
+// #include class definitions for all members.
+// For example, m_settings has an internal dependency on univalue.
+ArgsManager::ArgsManager() {}
+ArgsManager::~ArgsManager() {}
 
 const std::set<std::string> ArgsManager::GetUnsuitableSectionOnlyArgs() const
 {

src/util/system.h

@@ -192,6 +192,7 @@ protected:
 
 public:
     ArgsManager();
+    ~ArgsManager();
 
     /**
      * Select the network in use