fix group element text clipping

fixes group element header text clipping outside of the header and into the settings icon (if there is one).
Also some extra code to handle script editor, as that displays some extra icons in the header.

Source/Engine/UI/GUI/Panels/DropPanel.cs

@@ -361,7 +361,7 @@ namespace FlaxEngine.GUI
             var style = Style.Current;
             var enabled = EnabledInHierarchy;
 
-            // Paint Background
+            // Draw Background
             var backgroundColor = BackgroundColor;
             if (backgroundColor.A > 0.0f)
             {
@@ -388,7 +388,7 @@ namespace FlaxEngine.GUI
                     ArrowImageOpened?.Draw(dropDownRect, arrowColor);
             }
 
-            // Text
+            // Header text
             var textRect = new Rectangle(textLeft, 0, Width - textLeft, HeaderHeight);
             _headerTextMargin.ShrinkRectangle(ref textRect);
             var textColor = HeaderTextColor;
@@ -397,7 +397,9 @@ namespace FlaxEngine.GUI
                 textColor *= 0.6f;
             }
 
+            Render2D.PushClip(textRect);
             Render2D.DrawText(HeaderTextFont.GetFont(), HeaderTextMaterial, HeaderText, textRect, textColor, TextAlignment.Near, TextAlignment.Center);
+            Render2D.PopClip();
 
             if (!_isClosed && EnableContainmentLines)
             {