patch 8.1.1996: more functions can be used as methods

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index 9f43732..110cecb 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -504,7 +504,7 @@
     let set[0]['conceal'] = 5
     let exp[0]['conceal'] = '5'
   endif
-  call setmatches(set)
+  eval set->setmatches()
   call assert_equal(exp, getmatches())
 endfunc