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: #15818

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/cmdexpand.c b/src/cmdexpand.c
index c7c42ab..e563d22 100644
--- a/src/cmdexpand.c
+++ b/src/cmdexpand.c
@@ -360,7 +360,8 @@
 	compl_match_array[i].pum_info = NULL;
 	compl_match_array[i].pum_extra = NULL;
 	compl_match_array[i].pum_kind = NULL;
-	compl_match_array[i].pum_user_hlattr = -1;
+	compl_match_array[i].pum_user_abbr_hlattr = -1;
+	compl_match_array[i].pum_user_kind_hlattr = -1;
     }
 
     // Compute the popup menu starting column