Added Luminance property and updated authors

-Added public Luminance property in Color.cs to calculate colour brightness.
-Refactored Dropdown.cs to use Luminance instead of manual calculation.
-Updated author list in AboutDialog.cs by adding ‘Michael Salvini’.

Source/Editor/Windows/AboutDialog.cs

@@ -98,6 +98,7 @@ namespace FlaxEditor.Windows
                 "Chandler Cox",
                 "Ari Vuollet",
                 "Vincent Saarmann",
+                "Michael Salvini",
             });
             authors.Sort();
             var authorsLabel = new Label(4, topParentControl.Bottom + 20, Width - 8, 70)

Source/Engine/Core/Math/Color.cs

@@ -82,6 +82,11 @@ namespace FlaxEngine
             }
         }
 
+        /// <summary>
+        ///  Gets the brightness of the color
+        /// </summary>
+        public float Luminance => R * 0.299f + G * 0.587f + B * 0.114f;
+
         /// <summary>
         /// Returns the minimum color component value: Min(r,g,b).
         /// </summary>

Source/Engine/UI/GUI/Common/Dropdown.cs

@@ -588,7 +588,6 @@ namespace FlaxEngine.GUI
                 AutoFocus = false,
                 Size = size,
             };
-            float brightness = TextColorHighlighted.R * 0.299f + TextColorHighlighted.G * 0.587f + TextColorHighlighted.B * 0.114f;
             var label = new DropdownLabel
             {
                 AutoFocus = true,
@@ -596,7 +595,7 @@ namespace FlaxEngine.GUI
                 Size = new Float2(size.X - margin, size.Y),
                 Font = Font,
                 TextColor = TextColor * 0.9f,
-                TextColorHighlighted = brightness < 0.05f ? Color.Lerp(TextColorHighlighted, Color.White, 0.3f) : TextColorHighlighted,
+                TextColorHighlighted = TextColorHighlighted.Luminance < 0.05f ? Color.Lerp(TextColorHighlighted, Color.White, 0.3f) : TextColorHighlighted,
                 HorizontalAlignment = HorizontalAlignment,
                 VerticalAlignment = VerticalAlignment,
                 Text = _items[i],