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: #15348

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/structs.h b/src/structs.h
index 2e8efa8..32c35b7 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4472,7 +4472,7 @@
     char_u	*pum_info;	  // extra info
     int		pum_score;	  // fuzzy match score
     int		pum_idx;	  // index of item before sorting by score
-    int		pum_extrahlattr;  // extra highlight group attr for combine
+    int		pum_user_hlattr;  // highlight attribute to combine with
 } pumitem_T;
 
 /*