patch 8.1.0166: using dict_add_nr_str() is clumsy

Problem:    Using dict_add_nr_str() is clumsy.
Solution:   Split into two functions. (Ozaki Kiichi, closes #3154)
diff --git a/src/undo.c b/src/undo.c
index be4e22e..b3a6276 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3567,14 +3567,14 @@
 	dict = dict_alloc();
 	if (dict == NULL)
 	    return;
-	dict_add_nr_str(dict, "seq", uhp->uh_seq, NULL);
-	dict_add_nr_str(dict, "time", (long)uhp->uh_time, NULL);
+	dict_add_number(dict, "seq", uhp->uh_seq);
+	dict_add_number(dict, "time", (long)uhp->uh_time);
 	if (uhp == curbuf->b_u_newhead)
-	    dict_add_nr_str(dict, "newhead", 1, NULL);
+	    dict_add_number(dict, "newhead", 1);
 	if (uhp == curbuf->b_u_curhead)
-	    dict_add_nr_str(dict, "curhead", 1, NULL);
+	    dict_add_number(dict, "curhead", 1);
 	if (uhp->uh_save_nr > 0)
-	    dict_add_nr_str(dict, "save", uhp->uh_save_nr, NULL);
+	    dict_add_number(dict, "save", uhp->uh_save_nr);
 
 	if (uhp->uh_alt_next.ptr != NULL)
 	{