Support GIGA multi-printhead configuration options (#13901)

* Support GIGA multi-printhead configuration options

* Removed unused G-code comments.

* Added parallel_printheads_count option to configure parallel printhead count.

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Co-authored-by: SoftFever <softfeverever@gmail.com>

src/slic3r/GUI/Field.hpp

@@ -190,6 +190,7 @@ public:
     /// Call the attached m_fn_edit_value method.
 	void			on_edit_value();
 
+    virtual void propagate_value(){}
 public:
     /// parent wx item, opportunity to refactor (probably not necessary - data duplication)
     wxWindow*		m_parent {nullptr};
@@ -317,7 +318,7 @@ public:
     void BUILD() override;
     bool value_was_changed();
     // Propagate value from field to the OptionGroupe and Config after kill_focus/ENTER
-    void propagate_value();
+    virtual void propagate_value() override;
     wxWindow* window {nullptr};
 
     void	set_value(const std::string& value, bool change_event = false) {