DolphinQt/Config/ARCodeWidget: Use forward declarations where applicable

Avoids propagating headers into scopes where they're not necessary.

Also uncovered reliance on an indirect inclusion within
CheatsManager.cpp, which is now fixed.

Source/Core/DolphinQt/CheatsManager.cpp

@@ -21,6 +21,7 @@
 #include <QTableWidget>
 #include <QVBoxLayout>
 
+#include "Core/ActionReplay.h"
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
 #include "Core/Debugger/PPCDebugInterface.h"

Source/Core/DolphinQt/Config/ARCodeWidget.cpp

@@ -43,6 +43,8 @@ ARCodeWidget::ARCodeWidget(const UICommon::GameFile& game, bool restart_required
   OnSelectionChanged();
 }
 
+ARCodeWidget::~ARCodeWidget() = default;
+
 void ARCodeWidget::CreateWidgets()
 {
   m_warning = new CheatWarningWidget(m_game_id, m_restart_required, this);

Source/Core/DolphinQt/Config/ARCodeWidget.h

@@ -10,7 +10,11 @@
 #include <vector>
 
 #include "Common/CommonTypes.h"
-#include "Core/ActionReplay.h"
+
+namespace ActionReplay
+{
+struct ARCode;
+}
 
 namespace UICommon
 {
@@ -28,6 +32,7 @@ class ARCodeWidget : public QWidget
   Q_OBJECT
 public:
   explicit ARCodeWidget(const UICommon::GameFile& game, bool restart_required = true);
+  ~ARCodeWidget() override;
 
   void AddCode(ActionReplay::ARCode code);