Add arnsholt++ nqp::sethllconfig implementation.

Also teach it a bunch of extra HLL-interop related keys.
Start of new HLL-interop infrastructure.

Builds upon the Parrot HLL identifiers. This mechanism will be used to
fix various Rakudo issues when NQP-defiend objects are encountered. It
will also replace the special-case perl6ize_type with a more general
and more portable mechanism, that can work in an environment where all
objects are 6model objects.
Code object mapping support.
Interop mapping support for 6model objects.