[editor] Check OSM max char length in value validation

Signed-off-by: map-per <map-per@gmx.de>

libs/indexer/editable_map_object.hpp

@@ -70,6 +70,7 @@ class EditableMapObject : public MapObject
 {
 public:
   static uint8_t constexpr kMaximumLevelsEditableByUsers = 50;
+  static int constexpr kMaximumOsmChars = 255;
 
   bool IsNameEditable() const;
   bool IsAddressEditable() const;