Cleanup: use explicit enum type for duplicate option of BKE_object_duplicate

Using enum type itself in implementations, and uint in headers (as using
enums types in headers is a pain when enum are not defined and used in a
single same header file...).

source/blender/editors/curve/editcurve.c

@@ -1432,7 +1432,7 @@ static int separate_exec(bContext *C, wmOperator *op)
     /* 2. Duplicate the object and data. */
 
     /* Take into account user preferences for duplicating actions. */
-    short dupflag = (U.dupflag & USER_DUP_ACT);
+    const eDupli_ID_Flags dupflag = (U.dupflag & USER_DUP_ACT);
 
     newbase = ED_object_add_duplicate(bmain, scene, view_layer, oldbase, dupflag);
     DEG_relations_tag_update(bmain);