Pcbnew: DRAWSEGMENT polygonal shape: fix drawings in Legacy mode. Add IsPolygonFilled() to know if the polygon is filled or not.

IsPolygonFilled() replaces the hard coded comparisob with Edge_Cut in code.
For now the polygon is not filled only on Edge_Cut layer.

But in the future, it could be an option for other layers.

pcbnew/plot_brditems_plotter.cpp

@@ -534,7 +534,7 @@ void BRDITEMS_PLOTTER::Plot_1_EdgeModule( EDGE_MODULE* aEdge )
                 cornerList.push_back( corner );
             }
 
-            if( m_layerMask[ Edge_Cuts ] )
+            if( !aEdge->IsPolygonFilled() )
             {
                 for( size_t i = 1; i < cornerList.size(); i++ )
                 {
@@ -777,7 +777,7 @@ void BRDITEMS_PLOTTER::PlotDrawSegment( DRAWSEGMENT* aSeg )
 
     case S_POLYGON:
         {
-            if( m_layerMask[ Edge_Cuts ] )
+            if( !aSeg->IsPolygonFilled() )
             {
                 for( auto it = aSeg->GetPolyShape().IterateSegments( 0 ); it; it++ )
                 {