vim-patch:9.1.0629: Rename of pum hl_group is incomplete

Problem:  Rename of pum hl_group is incomplete in source.
Solution: Also rename the test function.  Rename to user_hlattr in code
          to avoid confusion with pum_extra.  Add test with matched text
          highlighting (zeertzjq).

closes: vim/vim#15348

4100852e09

src/nvim/cmdexpand.c

@@ -356,7 +356,7 @@ static int cmdline_pum_create(CmdlineInfo *ccline, expand_T *xp, char **matches,
       .pum_info = NULL,
       .pum_extra = NULL,
       .pum_kind = NULL,
-      .pum_extrahlattr = -1,
+      .pum_user_hlattr = -1,
     };
   }