patch 8.1.1915: 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_cindent.vim b/src/testdir/test_cindent.vim
index a8a2345..e12e457 100644
--- a/src/testdir/test_cindent.vim
+++ b/src/testdir/test_cindent.vim
@@ -121,9 +121,9 @@
   new
   setlocal cindent
   call setline(1, ['int main(void)', '{', 'return 0;', '}'])
-  call assert_equal(cindent(0), -1)
-  call assert_equal(cindent(3), &sw)
-  call assert_equal(cindent(line('$')+1), -1)
+  call assert_equal(-1, cindent(0))
+  call assert_equal(&sw, 3->cindent())
+  call assert_equal(-1, cindent(line('$')+1))
   bwipe!
 endfunc