Move File::Temp, File::Path, File::Basename, and parent to perl-base

The module primarily being moved into the Essential set is File::Temp,
the others are pulled in as dependencies.

Securely creating a temporary file is both difficult and a reasonable
action for maintainer scripts to want to take, so it makes sense to have
that in the essential set. Using /usr/bin/mktemp from Perl programs is
unnecessarily hard and error-prone.

See https://lists.debian.org/debian-devel/2014/11/msg00216.html