Make AMS trays read-only in laser mode and add the gradient fill helper

src/slic3r/GUI/FilamentBitmapUtils.hpp

@@ -3,10 +3,17 @@
 
 #include <wx/bitmap.h>
 #include <wx/colour.h>
+#include <wx/dc.h>
+#include <wx/gdicmn.h>
 #include <vector>
 
 namespace Slic3r { namespace GUI {
 
+// Fills a rect with a west->east linear gradient by drawing solid 1px columns.
+// Use instead of wxDC::GradientFillLinear, whose CoreGraphics (CGShading) backend
+// fails to render on some macOS builds; solid fills are unaffected.
+void fill_gradient_rect_east(wxDC& dc, const wxRect& rect, const wxColour& from, const wxColour& to);
+
 enum class FilamentRenderMode {
     Single,
     Dual,