vim-patch:9.1.0771: completion attribute hl_group is confusing

Problem:  Currently completion attribute hl_group is combined with
          all items, which is redundant and confusing with kind_hlgroup
Solution: Renamed to abbr_hlgroup and combine it only with the abbr item
          (glepnir).

closes: vim/vim#15818

0fe17f8ffb

Co-authored-by: glepnir <glephunter@gmail.com>

src/nvim/cmdexpand.c

@@ -357,7 +357,8 @@ static int cmdline_pum_create(CmdlineInfo *ccline, expand_T *xp, char **matches,
       .pum_info = NULL,
       .pum_extra = NULL,
       .pum_kind = NULL,
-      .pum_user_hlattr = -1,
+      .pum_user_abbr_hlattr = -1,
+      .pum_user_kind_hlattr = -1,
     };
   }