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_cd.vim b/src/testdir/test_cd.vim
index 3185954..e0dedfb 100644
--- a/src/testdir/test_cd.vim
+++ b/src/testdir/test_cd.vim
@@ -85,7 +85,7 @@
   call assert_equal('y', fnamemodify(getcwd(1, 2), ':t'))
   call assert_equal('z', fnamemodify(getcwd(3, 2), ':t'))
   tabnext | wincmd t
-  call chdir('..')
+  eval '..'->chdir()
   call assert_equal('Xdir', fnamemodify(getcwd(1, 2), ':t'))
   call assert_equal('Xdir', fnamemodify(getcwd(2, 2), ':t'))
   call assert_equal('z', fnamemodify(getcwd(3, 2), ':t'))