patch 8.1.2013: 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_listchars.vim b/src/testdir/test_listchars.vim
index a304c53..987ed66 100644
--- a/src/testdir/test_listchars.vim
+++ b/src/testdir/test_listchars.vim
@@ -25,7 +25,7 @@
   redraw!
   for i in range(1, 5)
     call cursor(i, 1)
-    call assert_equal([expected[i - 1]], ScreenLines(i, virtcol('$')))
+    call assert_equal([expected[i - 1]], ScreenLines(i, '$'->virtcol()))
   endfor
 
   set listchars-=trail:<