Implement wxWindow::GetWindowBorderSize() in wxQt

This notably fixes the appearance of wxSearchCtrl in this port.

Closes #24318.

include/wx/qt/window.h

@@ -112,6 +112,8 @@ public:
     virtual int GetScrollThumb( int orient ) const override;
     virtual int GetScrollRange( int orient ) const override;
 
+    virtual wxSize GetWindowBorderSize() const override;
+
         // scroll window to the specified position
     virtual void ScrollWindow( int dx, int dy,
                                const wxRect* rect = nullptr ) override;

src/qt/window.cpp

@@ -959,6 +959,30 @@ void wxWindowQt::SetWindowStyleFlag( long style )
     GetHandle()->setWindowFlags( qtFlags );
 }
 
+wxSize wxWindowQt::GetWindowBorderSize() const
+{
+    wxCoord border;
+    switch ( GetBorder() )
+    {
+        case wxBORDER_STATIC:
+        case wxBORDER_SIMPLE:
+        case wxBORDER_SUNKEN:
+        case wxBORDER_RAISED:
+        case wxBORDER_THEME:
+            border = 1;
+            break;
+
+        default:
+            wxFAIL_MSG( wxT("unknown border style") );
+            wxFALLTHROUGH;
+
+        case wxBORDER_NONE:
+            border = 0;
+    }
+
+    return 2 * wxSize(border, border);
+}
+
 void wxWindowQt::SetExtraStyle( long exStyle )
 {
     long exStyleOld = GetExtraStyle();