3D Viewer: fix incorrect render of plated copper of texts.

Previously, with option "Use bare copper color for unplated copper", the
plated area of texts were drawn using their bounding box.

(cherry picked from commit becaba531b
and from commit ca5f867957)

3d-viewer/3d_canvas/create_layer_items.cpp

@@ -643,12 +643,33 @@ void BOARD_ADAPTER::createLayers( REPORTER* aStatusReporter )
             // add also this shape to the plated copper polygon list if required
             if( cfg.differentiate_plated_copper )
             {
-                if( layer == F_Cu )
-                    item->TransformShapeToPolygon( *m_frontPlatedCopperPolys, F_Cu,
-                                                    0, maxError, ERROR_INSIDE );
-                else if( layer == B_Cu )
-                    item->TransformShapeToPolygon( *m_backPlatedCopperPolys, B_Cu,
-                                                    0, maxError, ERROR_INSIDE );
+                // Note: for TEXT and TEXTBOX, TransformShapeToPolygon returns the bounding
+                // box shape, not the exact text shape. So it is not used for these items
+                if( layer == F_Cu || layer == B_Cu )
+                {
+                    SHAPE_POLY_SET* platedCopperPolys = layer == F_Cu
+                                                            ? m_frontPlatedCopperPolys
+                                                            : m_backPlatedCopperPolys;
+
+                    if( item->Type() == PCB_TEXTBOX_T )
+                    {
+                        PCB_TEXTBOX* text_box = static_cast<PCB_TEXTBOX*>( item );
+                        text_box->TransformTextToPolySet( *platedCopperPolys,
+                                                           0, maxError, ERROR_INSIDE );
+                        // Add box outlines
+                        text_box->PCB_SHAPE::TransformShapeToPolygon( *platedCopperPolys, layer,
+                                                                       0, maxError, ERROR_INSIDE );
+                    }
+                    else if( item->Type() == PCB_TEXT_T )
+                    {
+                        static_cast<PCB_TEXT*>( item )->TransformTextToPolySet(
+                                                                *platedCopperPolys,
+                                                                0, maxError, ERROR_INSIDE );
+                    }
+                    else
+                        item->TransformShapeToPolygon( *platedCopperPolys, layer,
+                                                        0, maxError, ERROR_INSIDE );
+                }
             }
         }
     }