Harden #5070 fix + disable dead change_part_type() via #if 0 (#13281)

* Restore SVG/text→Support crash guard (#5070), disable change_part_type()

The crash fix from #5070 prevented converting SVG/text modifiers to Support
Blocker / Support Enforcer by hiding those entries in the old SingleChoiceDialog
opened from ObjectList::change_part_type(). When the "Change type" UI was
reworked into a submenu that calls ObjectList::set_volume_type() directly, the
guard was left behind in the unused change_part_type() path -- the submenu path
had no protection, silently reintroducing the #5070 crash on the submenu route
(ModelVolume::set_type() does not clear text_configuration / emboss_shape, so
the stale emboss state stays attached to a support volume).

- Guard set_volume_type(): reject SUPPORT_BLOCKER / SUPPORT_ENFORCER when any
  selected volume is SVG or text, showing the same error as before.
- Wrap ObjectList::change_part_type() in #if 0 instead of deleting it: the
  function is unused since the submenu rework, but keeping it in commented-out
  form preserves traceability with upstream Bambu Studio (avoids merge
  conflicts on each BBL sync). Suggested by RF47, confirmed by ianalexis.

* Log instead of showing user error; action guard is defense-in-depth only

Per review feedback from RF47: with the UI-side guard in #13120, the
set_volume_type() action-time check is a pure safety net -- a healthy UI
should never let the user reach it. Showing a modal error dialog would
therefore either confuse a user who did nothing wrong (if the UI guard
is bypassed by a future refactor/plugin/shortcut) or be dead code at
runtime. Log the event for developers instead, keep the early return so
the crash is still prevented.

src/slic3r/GUI/GUI_ObjectList.hpp

@@ -413,7 +413,9 @@ public:
     bool fix_cut_selection(wxDataViewItemArray &sels);
 
     ModelVolume* get_selected_model_volume();
+#if 0 // ORCA: disabled alongside definition in GUI_ObjectList.cpp (see #if 0 block there)
     void change_part_type();
+#endif
 	void set_volume_type(ModelVolumeType new_type);
     ModelVolumeType get_selected_volume_type();