improve to_json(StyleP)

src/data/field/choice.hpp

@@ -111,7 +111,10 @@ enum ChoicePopupStyle
 {  POPUP_MENU
 ,  POPUP_DROPDOWN
 ,  POPUP_DROPDOWN_IN_PLACE
-};
+};
+
+String popup_style_to_string(const ChoicePopupStyle&);
+
 // How should a choice value be rendered?
 enum ChoiceRenderStyle
 {  RENDER_TEXT            = 0x01  // render the name as text
@@ -129,6 +132,8 @@ enum ChoiceRenderStyle
 ,  RENDER_BOTH_LIST       = RENDER_LIST      | RENDER_BOTH
 };
 
+String render_style_to_string(const ChoiceRenderStyle&);
+
 enum ThumbnailStatus
 {  THUMB_NOT_MADE // there is no image
 ,  THUMB_OK       // image is ok