vim-patch:8.0.1332: enhance quickfix highlighting #10259

Problem:    Highlighting in quickfix window could be better. (Axel Bender)
Solution:   Use the qfSeparator highlight item. (Yegappan Lakshmanan)
93a32e2ec4

This adds `syn_name2attr` already (from previous patch 8.0.1123,
vim/vim@1b9645de3).

src/nvim/syntax.c

@@ -7341,6 +7341,18 @@ int syn_name2id(const char_u *name)
   return i + 1;
 }
 
+/// Lookup a highlight group name and return its attributes.
+/// Return zero if not found.
+int syn_name2attr(char_u *name)
+{
+  int id = syn_name2id(name);
+
+  if (id != 0) {
+    return syn_id2attr(syn_get_final_id(id));
+  }
+  return 0;
+}
+
 /*
  * Return TRUE if highlight group "name" exists.
  */