Feature: Improve add-on init dispatch

Handle different add-on `init()` signatures in a generic and type safe way. An adapter is selected at compile-time based on the signature of the init function. The adapter is stored in the module struct. At run-time the adapter unpacks the users init function and provides the requested arguments.

This is related to #8802.
Good catch.

It is perfectly valid but the compiler will not inline, obviously. We _want_ the function pointer (stupid me). I'll remove the keyword `inline` from `registerAddon`.