DolphinQt/Config/GeckoCodeWidget: Use forward declarations where applicable

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

Source/Core/DolphinQt/Config/GeckoCodeWidget.cpp

@@ -19,6 +19,7 @@
 #include "Common/IniFile.h"
 
 #include "Core/ConfigManager.h"
+#include "Core/GeckoCode.h"
 #include "Core/GeckoCodeConfig.h"
 
 #include "DolphinQt/Config/CheatCodeEditor.h"
@@ -46,6 +47,8 @@ GeckoCodeWidget::GeckoCodeWidget(const UICommon::GameFile& game, bool restart_re
   UpdateList();
 }
 
+GeckoCodeWidget::~GeckoCodeWidget() = default;
+
 void GeckoCodeWidget::CreateWidgets()
 {
   m_warning = new CheatWarningWidget(m_game_id, m_restart_required, this);