- Added official support for a CTE used by the SELECT present

- Added official support for a CTE used by the SELECT present
inside of :meth:`.Insert.from_select`.  This behavior worked
accidentally up until 0.9.9, when it no longer worked due to
unrelated changes as part of :ticket:`3248`.   Note that this
is the rendering of the WITH clause after the INSERT, before the
SELECT; the full functionality of CTEs rendered at the top
level of INSERT, UPDATE, DELETE is a new feature targeted for a
later release.
fixes #3418

(cherry picked from commit eb1bb84fbc10c801c7269a3d38c9e0235327857e)