run sentinel server side fns outside of VALUES

run sentinel server side fns outside of VALUES

Fixed the structure of the SQL string used for the
:ref:`engine_insertmanyvalues` feature when an explicit sequence with
``nextval()`` is used. The SQL function invocation for the sequence has
been moved from being rendered inline within each tuple inside of VALUES to
being rendered once in the SELECT that reads from VALUES. This change
ensures the function is invoked in the correct order as rows are processed,
rather than assuming PostgreSQL will execute inline function calls within
VALUES in a particular order. While current PostgreSQL versions appear to
handle the previous approach correctly, the database does not guarantee
this behavior for future versions.

Fixes: #13015
Change-Id: Ia0a2a4e8f89e21852d7cb550dfa5d9ea9447b590