patch 8.1.1996: 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_tabpage.vim b/src/testdir/test_tabpage.vim
index c8ac114..020fe27 100644
--- a/src/testdir/test_tabpage.vim
+++ b/src/testdir/test_tabpage.vim
@@ -34,7 +34,7 @@
   tabnew
   tabfirst
   call settabvar(2, 'val_num', 100)
-  call settabvar(2, 'val_str', 'SetTabVar test')
+  eval 'SetTabVar test'->settabvar(2, 'val_str')
   call settabvar(2, 'val_list', ['red', 'blue', 'green'])
   "
   call assert_true(gettabvar(2, 'val_num') == 100 && gettabvar(2, 'val_str') == 'SetTabVar test' && gettabvar(2, 'val_list') == ['red', 'blue', 'green'])
@@ -183,7 +183,7 @@
   let s:li = split(join(map(copy(winr), 'gettabwinvar('.tabn.', v:val, "a")')), '\s\+')
   call assert_equal(['a', 'a'], s:li)
   let s:li = []
-  C call map(copy(winr), 'settabwinvar('.tabn.', v:val, ''a'', v:val*2)')
+  C call map(copy(winr), '(v:val*2)->settabwinvar(' .. tabn .. ', v:val, ''a'')')
   let s:li = split(join(map(copy(winr), 'gettabwinvar('.tabn.', v:val, "a")')), '\s\+')
   call assert_equal(['2', '4'], s:li)