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>

runtime/lua/vim/lsp/completion.lua

@@ -272,7 +272,7 @@ function M._lsp_to_complete_items(result, prefix, client_id)
         icase = 1,
         dup = 1,
         empty = 1,
-        hl_group = hl_group,
+        abbr_hlgroup = hl_group,
         user_data = {
           nvim = {
             lsp = {