GDExtension: Use Uninitialized*Ptr for constructors/converters using placement new

[Bromeon]

A few methods in the GDExtension header construct their destination in-place, but the parameters are not declared using the Uninitialized* pointer types.

See godot-cpp PR: godotengine/godot-cpp#1148

---

Below are the relevant sections where placement new is used.

TypePtr constructors:

godot/core/variant/variant_construct.h

Lines 45 to 54 in 116f783

	template <class T>
	struct PtrConstruct {};
	#define MAKE_PTRCONSTRUCT(m_type) \
	template <> \
	struct PtrConstruct<m_type> { \
	_FORCE_INLINE_ static void construct(const m_type &p_value, void *p_ptr) { \
	memnew_placement(p_ptr, m_type(p_value)); \
	} \
	};

VariantPtr <-> TypePtr conversions:

godot/core/variant/variant_internal.h

Lines 1535 to 1546 in 116f783

	template <class T>
	struct VariantTypeConstructor {
	_FORCE_INLINE_ static void variant_from_type(void *r_variant, void *p_value) {
	// r_variant is provided by caller as uninitialized memory
	memnew_placement(r_variant, Variant(*((T *)p_value)));
	}
	_FORCE_INLINE_ static void type_from_variant(void *r_value, void *p_variant) {
	// r_value is provided by caller as uninitialized memory
	memnew_placement(r_value, T(VariantInternalAccessor<T>::get(reinterpret_cast<Variant *>(p_variant))));
	}
	};

[touilleMan]

O_o I'm very puzzled how I missed that (especially given VariantPtr <-> TypePtr with uninitialized input was introduced in my PR !)

Anyway great job 🥳 🎉

[akien-mga]

Thanks!