patch 8.1.1921: 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_vimscript.vim b/src/testdir/test_vimscript.vim
index dc4df44..8dc00f2 100644
--- a/src/testdir/test_vimscript.vim
+++ b/src/testdir/test_vimscript.vim
@@ -638,7 +638,7 @@
 	if v:errmsg == ""
 	    Xout "Message missing."
 	else
-	    let v:errmsg = escape(v:errmsg, '"')
+	    let v:errmsg = v:errmsg->escape('"')
 	    Xout "Unexpected message:" v:errmsg
 	endif
     endif