patch 8.1.2013: 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_execute_func.vim b/src/testdir/test_execute_func.vim
index f3d7e37..f81a86b 100644
--- a/src/testdir/test_execute_func.vim
+++ b/src/testdir/test_execute_func.vim
@@ -91,7 +91,7 @@
   if has('textprop')
     let popupwin = popup_create('the popup win', {'line': 2, 'col': 3})
     redraw
-    let line = win_execute(popupwin, 'echo getline(1)')
+    let line = 'echo getline(1)'->win_execute(popupwin)
     call assert_match('the popup win', line)
 
     call popup_close(popupwin)