Add option for hiding / showing gridlines (#10545)

Might be useful who want to use custom grid line system with textures. or a clean look

### PROBLEM / SCENARIOS
• Custom made textures overlapping with grid system. so it might be confusing for user if want to use specific markings
• User may found its a distracting item and wants a clean look

### SOLUTION
added to view menu
<img width="477" height="434" alt="Screenshot-20251230192707" src="https://github.com/user-attachments/assets/e298d9b2-5f8f-4e33-af22-ea7c84c9b5b8" />

added to canvas menu
<img width="278" height="297" alt="Screenshot-20251230192717" src="https://github.com/user-attachments/assets/a9952408-a361-4e64-ad9a-72e2480c74cf" />

Clean look without gridlines
<img width="1669" height="1157" alt="Screenshot-20250827144140" src="https://github.com/user-attachments/assets/9229f330-9543-4d39-a8fc-01deb9b61336" />

<img width="1669" height="1157" alt="Screenshot-20250827144212" src="https://github.com/user-attachments/assets/ab3848fb-74d7-4618-8bc7-0cdff10a3804" />


Few Examples with custom made textures / markings without gridlines
<img width="1669" height="1157" alt="Screenshot-20250827140008" src="https://github.com/user-attachments/assets/5d7b17ab-e97a-489c-9e4d-99157a37b6b7" />

<img width="1669" height="1157" alt="Screenshot-20250827141904" src="https://github.com/user-attachments/assets/a7e0f360-a85a-489d-9bc2-39286984643a" />

src/slic3r/GUI/GLCanvas3D.cpp

@@ -8637,7 +8637,13 @@ void GLCanvas3D::_render_canvas_toolbar()
             [this]{toggle_world_axes_visibility(false);}
         );
 
-        // will add an option for gridlines in here
+        create_menu_item( "Gridlines",
+            m_canvas_type != ECanvasType::CanvasAssembleView, // not work on assembly
+            wxGetApp().show_plate_gridlines(),
+            [this]{wxGetApp().toggle_show_plate_gridlines();}
+        );
+
+        ImGui::Separator();
 
         create_menu_item( "Labels",
             m_canvas_type == ECanvasType::CanvasView3D, // work only on prepare