Pcbnew: refinement for commit 8057f7d4: Keep edge.cuts dimmed in hide/dim mode

Because in dim or hide non active layers mode items on these layer are not
selectable, dim items on edge.cuts layer (when non active) are also shown dimmed.

pcbnew/pcb_painter.cpp

@@ -437,18 +437,27 @@ COLOR4D PCB_RENDER_SETTINGS::GetColor( const BOARD_ITEM* aItem, int aLayer ) con
 
         if( !isActive )
         {
-            // Graphics on Edge_Cuts layers are not dimmed or hidden because they are
-            // in fact on all layers
+            // Graphics on Edge_Cuts layer are not fully dimmed or hidden because they are
+            // useful when working on another layer
+            // We could use a dim factor = m_hiContrastFactor, but to have a sufficient
+            // contrast whenever m_hiContrastFactor value, we clamp the factor to 0.3f
+            // (arbitray choice after tests)
+            float dim_factor_Edge_Cuts = std::max( m_hiContrastFactor, 0.3f );
+
             if( m_ContrastModeDisplay == HIGH_CONTRAST_MODE::HIDDEN
                 || IsNetnameLayer( aLayer )
                 || hide )
             {
-                if( originalLayer != Edge_Cuts )
+                if( originalLayer == Edge_Cuts )
+                    color = color.Mix( m_layerColors[LAYER_PCB_BACKGROUND], dim_factor_Edge_Cuts );
+                else
                     color = COLOR4D::CLEAR;
             }
             else
             {
-                if( originalLayer != Edge_Cuts )
+                if( originalLayer == Edge_Cuts )
+                    color = color.Mix( m_layerColors[LAYER_PCB_BACKGROUND], dim_factor_Edge_Cuts );
+                else
                     color = color.Mix( m_layerColors[LAYER_PCB_BACKGROUND], m_hiContrastFactor );
 
                 // Reference images can't have their color mixed so just reduce the opacity a bit