DolphinQt/Settings: Replace includes with forward declarations

Avoids dragging in netplay-related headers where they aren't explicitly
necessary.

Source/Core/DolphinQt/NetPlay/MD5Dialog.cpp

@@ -13,6 +13,9 @@
 #include <QProgressBar>
 #include <QVBoxLayout>
 
+#include "Core/NetPlayClient.h"
+#include "Core/NetPlayServer.h"
+
 #include "DolphinQt/Settings.h"
 
 static QString GetPlayerNameFromPID(int pid)

Source/Core/DolphinQt/NetPlay/PadMappingDialog.cpp

@@ -3,15 +3,17 @@
 // Refer to the license.txt file included.
 
 #include "DolphinQt/NetPlay/PadMappingDialog.h"
-#include "DolphinQt/Settings.h"
-
-#include "Core/NetPlayClient.h"
 
 #include <QComboBox>
 #include <QDialogButtonBox>
 #include <QGridLayout>
 #include <QLabel>
 
+#include "Core/NetPlayClient.h"
+#include "Core/NetPlayServer.h"
+
+#include "DolphinQt/Settings.h"
+
 PadMappingDialog::PadMappingDialog(QWidget* parent) : QDialog(parent)
 {
   setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);

Source/Core/DolphinQt/Settings.cpp

@@ -19,6 +19,8 @@
 #include "Core/Config/MainSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
+#include "Core/NetPlayClient.h"
+#include "Core/NetPlayServer.h"
 
 #include "DolphinQt/GameList/GameListModel.h"
 #include "DolphinQt/QtUtils/QueueOnObject.h"
@@ -38,6 +40,8 @@ Settings::Settings()
   SetCurrentUserStyle(GetCurrentUserStyle());
 }
 
+Settings::~Settings() = default;
+
 Settings& Settings::Instance()
 {
   static Settings settings;

Source/Core/DolphinQt/Settings.h

@@ -11,9 +11,6 @@
 #include <QSettings>
 #include <QVector>
 
-#include "Core/NetPlayClient.h"
-#include "Core/NetPlayServer.h"
-
 namespace Core
 {
 enum class State;
@@ -24,6 +21,12 @@ namespace DiscIO
 enum class Language;
 }
 
+namespace NetPlay
+{
+class NetPlayClient;
+class NetPlayServer;
+}
+
 class GameListModel;
 class InputConfig;
 class QFont;
@@ -39,6 +42,8 @@ public:
   Settings(Settings&&) = delete;
   Settings& operator=(Settings&&) = delete;
 
+  ~Settings();
+
   static Settings& Instance();
   static QSettings& GetQSettings();