Add Feature to disable snapping to buildplate (#11801)

* identified code for snapping to buidlplate

* rename internal name to ensure_on_bed to be consistent, saves option in 2mf, finish Move UI, use in both ensure_on_bed() functions

* makes auto_drop a per-object setting, removes global setting

* remove adUndef, add auto_drop to constructor/serialize

* fixes drop() button

* add "auto_drop" checkmark to "load as single object" dialog,
nothing changes if auto_drop == yes || "load as single object",
if auto_drop == false and "load as single object" == false the objects now retain their relative position to each other

* retains auto_drop (and printable) state when assembling or splitting objects,
adds ObjectList::printable_state_changed()  overload to be able to only provide ModelObject* vector

* adds dialog when splitting to ask if auto_drop should be disabled,
only shows when auto_drop enabled and atleast one volume  floating

* adds arrow indicator on bounding box if auto_drop == false

* removes unneeded code, keeps "auto_drop" naming consistent

* makes for loop simpler in set_printable, set_auto_drop and get_auto_drop,
makes get_auto_drop const,
fixes wording in Snapshot text

---------

Co-authored-by: Hanno Witzleb <hannowitzleb@gmail.com>
Co-authored-by: SoftFever <softfeverever@gmail.com>
Co-authored-by: Ian Bassi <ian.bassi@outlook.com>

src/slic3r/GUI/Plater.hpp

@@ -643,7 +643,8 @@ public:
     void drop_selection();
     void search(bool plater_is_active, Preset::Type  type, wxWindow *tag, TextInput *etag, wxWindow *stag);
     void mirror(Axis axis);
-    void split_object();
+    void split_object(bool auto_drop = true);
+    void split_object(int obj_idx, bool auto_drop = true);
     void split_volume();
     void optimize_rotation();
     // find all empty cells on the plate and won't overlap with exclusion areas