perl: Modernize build, re-enable building external perl modules, remove microperl

This is basically a refactor of the old perl package.

- Modernize building
We're now using the infrastructure OpenWRT's buildroot provides more, both to integrate nicely and
make maintaining the package less painful. The main change here is that host-perl gets built using Host/* rules  instead of the old custom mechanism. It now also correctly installs into STAGING_DIR_HOST
instead of STAGING_DIR. It's built relocatable to make it play along in the SDK package

- Re-enable building external modules
This especially allows the oldpackages/lang/perl-* packages to be imported, which currently throw
nasty error messages. I will start importing them after this has been merged. This will then fix #17116.

- Remove microperl
Microperl is kind of meant to be used when bootstrapping a new perl installation, like miniperl I've removed
in the now-current perl package. It also lacks many system-specific features, which makes it not that
useful. So it's gone.

I've also bumped PKG_RELEASE to 2. Full build and basic functionality were tested for mipsel and arm targets.