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_bufwintabinfo.vim b/src/testdir/test_bufwintabinfo.vim
index 4e2c5d2..ee22ebd 100644
--- a/src/testdir/test_bufwintabinfo.vim
+++ b/src/testdir/test_bufwintabinfo.vim
@@ -47,7 +47,7 @@
     tabnew | let w3_id = win_getid()
     new | let w4_id = win_getid()
     vert new | let w5_id = win_getid()
-    call setwinvar(0, 'signal', 'green')
+    eval 'green'->setwinvar(0, 'signal')
     tabfirst
     let winlist = getwininfo()
     call assert_equal(5, len(winlist))