Require Perl 5.26.0

Require Perl 5.26.0

Our platform support policy states that we require "versions of
dependencies which are generally accepted as stable and supportable,
e.g., in line with the version used by other long-term-support
distributions".  Of Debian, Ubuntu, RHEL, and SLES, the four most common
distributions that provide LTS versions, the version with mainstream
long-term security support with the oldest Perl is 5.26.0 in SLES 15.6.

This is a major upgrade, since Perl 5.8.1, according to the Perl
documentation, was released in September of 2003.  It brings a lot of
new features that we can choose to use, such as s///r to return the
modified string, the postderef functionality, and subroutine signatures,
although the latter was still considered experimental until 5.36.

This change was made with the following one-liner, which intentionally
excludes modifying the vendored modules we include to avoid conflicts:

    git grep -l 'use 5.008001' | grep -v 'LoadCPAN/' | xargs perl -pi -e 's/use 5.008001/require v5.26/'

Use require instead of use to avoid changing the behavior as the latter
enables features and the former does not.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>