patch 8.1.1888: 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_hide.vim b/src/testdir/test_hide.vim
index 128b8ff..41b1a4a 100644
--- a/src/testdir/test_hide.vim
+++ b/src/testdir/test_hide.vim
@@ -37,7 +37,7 @@
   " :hide as a command
   hide
   call assert_equal([orig_bname, orig_winnr], [bufname(''), winnr('$')])
-  call assert_equal([1, 1], [buflisted('Xf1'), bufloaded('Xf1')])
+  call assert_equal([1, 1], ['Xf1'->buflisted(), 'Xf1'->bufloaded()])
   bwipeout! Xf1
 
   new Xf1