Instead of references. This is needed because those function pointers
are used in GDNative which needs to work with plain C, which doesn't
support passing parameters by reference.
- Initialize Object pointer to nullptr so it's not used by mistake.
- When setting an Object check if it's a reference so refcounting works
as intended.
Almost all instructions need variant arguments. With this change they
are loaded in an array before each instruction call. This makes the
addressing code be localized to less places, improving compilation
overhead and binary size by a small margin.
This should not affect performance.
