patch 8.1.1925: 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_cd.vim b/src/testdir/test_cd.vim
index e0dedfb..c3589b4 100644
--- a/src/testdir/test_cd.vim
+++ b/src/testdir/test_cd.vim
@@ -83,7 +83,7 @@
   tabfirst
   call chdir('..')
   call assert_equal('y', fnamemodify(getcwd(1, 2), ':t'))
-  call assert_equal('z', fnamemodify(getcwd(3, 2), ':t'))
+  call assert_equal('z', fnamemodify(3->getcwd(2), ':t'))
   tabnext | wincmd t
   eval '..'->chdir()
   call assert_equal('Xdir', fnamemodify(getcwd(1, 2), ':t'))