Implementation of array assignment support routines.
Given a pointer: If it is an Object, return that Object. If it is an interface, return the Object implementing the interface. If it is null, return null. Else, undefined crash
Attempts to cast Object o to class c. Returns o if successful, null if not.
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Licensed under the Boost License 1.0.
    https://dlang.org/phobos/rt_cast_.html