patch 8.1.1984: 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_pyx2.vim b/src/testdir/test_pyx2.vim
index 40e93c2..20199a4 100644
--- a/src/testdir/test_pyx2.vim
+++ b/src/testdir/test_pyx2.vim
@@ -34,7 +34,7 @@
 
 func Test_pyxeval()
   pyx import sys
-  call assert_match(s:py2pattern, split(pyxeval('sys.version'))[0])
+  call assert_match(s:py2pattern, split('sys.version'->pyxeval())[0])
 endfunc