Render VALUES within composed MySQL on duplicate key expressions

Render VALUES within composed MySQL on duplicate key expressions

Fixed issue in MySQL :meth:`.mysql.Insert.on_duplicate_key_update` construct
where using a SQL function or other composed expression for a column argument
would not properly render the ``VALUES`` keyword surrounding the column
itself.

Fixes: #5173
Change-Id: I16d39c2fdb8bbb7f3d1b2ffdd20e1bf69359ab75
(cherry picked from commit 57b2aae0d9efe91c2338e5a762e04366f86c2651)