Add Expert user mode (#13348)

Add Expert user mode with three-way mode switch. the old ModeButton has been removed.

Co-authored-by: Copilot <copilot@github.com>

src/libslic3r/Config.hpp

@@ -199,6 +199,7 @@ enum ConfigOptionType {
 enum ConfigOptionMode {
     comSimple = 0,
     comAdvanced,
+    comExpert,
     comDevelop,
 };