*/perl-*: standardize _pkgreal & expand source URL

This MR touches only 3 fields _pkgreal, source, and builddir.

Additionally, it also removes a couple of cd "$builddir" commands that are no longer needed, corrects a few cases where $pkgver was erroneously included in _realname (which is now standardized to _pkgreal), and fixes lint errors (missing default_prepare and shellcheck SC2035/SC2115).

The reason for choosing _pkgreal is because that is what apkbuild-cpan uses, and standardizing on that for the CPAN aports will allow us to simplify this piece of code that tries to guess which name is used (all new aports generated by apkbuild-cpan already use _pkgreal).

This is a first step towards being able to run apkbuild-cpan recreate over these aports to upgrade them to a newer template.