FIX:add "is_new_project_in_gcode3mf" api in .gcode.3mf

jira: STUDIO-9437
Change-Id: I5deb03cb535d3099ecadb1ce626fc632f65cd814
(cherry picked from commit 60fde9ca0135acb6c67302aa929f3fe975044c59)

src/slic3r/GUI/Plater.hpp

@@ -161,6 +161,7 @@ public:
     void change_filament(size_t from_id, size_t to_id);  // 0 base
     void edit_filament();
     void add_custom_filament(wxColour new_col);
+    bool is_new_project_in_gcode3mf();
     // BBS
     void on_bed_type_change(BedType bed_type);
     void load_ams_list(std::string const & device, MachineObject* obj);