LibGUI+PixelPaint: Move virtual destructors out-of-line for Clang 17

Author: https://github.com/BertalanD
Commit: 8366c9f55a
Pull-request: https://github.com/SerenityOS/serenity/pull/23960
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/DanShaders
Reviewed-by: https://github.com/alimpfard

Userland/Libraries/LibGUI/MultiView.cpp

@@ -50,6 +50,8 @@ MultiView::MultiView()
     set_view_mode(ViewMode::Icon);
 }
 
+MultiView::~MultiView() = default;
+
 void MultiView::set_view_mode(ViewMode mode)
 {
     if (m_view_mode == mode)

Userland/Libraries/LibGUI/MultiView.h

@@ -18,7 +18,7 @@ namespace GUI {
 class MultiView final : public GUI::StackWidget {
     C_OBJECT(MultiView)
 public:
-    virtual ~MultiView() override = default;
+    virtual ~MultiView() override;
 
     Function<void()> on_selection_change;
     Function<void(ModelIndex const&)> on_activation;