Move snowball_create.sql creation into perl file

Move snowball_create.sql creation into perl file

This is in preparation for building postgres with meson / ninja.

We already have duplicated code for this between the make and msvc
builds. Adding a third copy seems like a bad plan, thus move the generation
into a perl script.

As we don't want to rely on perl being available for builds from tarballs,
generate the file during distprep.

Author: Peter Eisentraut <[email protected]>
Author: Andres Freund <[email protected]>
Discussion: https://postgr.es/m/5e216522-ba3c-f0e6-7f97-5276d0270029@enterprisedb.com