Revert "Make freed object different than null in comparison operators"

This reverts commit 150b50cfcde95f74419ade2811d963224e96fc98.

As discussed with the GDScript team, this has some implications which aren't
fully consensual yet, and which we want to revisit.

For now we revert to the 4.2 behavior for the 4.3 release, to avoid breaking
user expectations.

core/variant/variant.cpp

@@ -951,7 +951,7 @@ bool Variant::is_zero() const {
 			return *reinterpret_cast<const ::RID *>(_data._mem) == ::RID();
 		}
 		case OBJECT: {
-			return get_validated_object() == nullptr;
+			return _get_obj().obj == nullptr;
 		}
 		case CALLABLE: {
 			return reinterpret_cast<const Callable *>(_data._mem)->is_null();

core/variant/variant_op.h

@@ -548,14 +548,14 @@ public:
 class OperatorEvaluatorEqualObject {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		const ObjectID &a = VariantInternal::get_object_id(&p_left);
-		const ObjectID &b = VariantInternal::get_object_id(&p_right);
+		const Object *a = p_left.get_validated_object();
+		const Object *b = p_right.get_validated_object();
 		*r_ret = a == b;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		const ObjectID &a = VariantInternal::get_object_id(left);
-		const ObjectID &b = VariantInternal::get_object_id(right);
+		const Object *a = left->get_validated_object();
+		const Object *b = right->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = a == b;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {
@@ -567,12 +567,12 @@ public:
 class OperatorEvaluatorEqualObjectNil {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		const Object *a = p_left.operator Object *();
+		const Object *a = p_left.get_validated_object();
 		*r_ret = a == nullptr;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		const Object *a = left->operator Object *();
+		const Object *a = left->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = a == nullptr;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {
@@ -584,12 +584,12 @@ public:
 class OperatorEvaluatorEqualNilObject {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		const Object *b = p_right.operator Object *();
+		const Object *b = p_right.get_validated_object();
 		*r_ret = nullptr == b;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		const Object *b = right->operator Object *();
+		const Object *b = right->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = nullptr == b;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {
@@ -619,14 +619,14 @@ public:
 class OperatorEvaluatorNotEqualObject {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		const ObjectID &a = VariantInternal::get_object_id(&p_left);
-		const ObjectID &b = VariantInternal::get_object_id(&p_right);
+		Object *a = p_left.get_validated_object();
+		Object *b = p_right.get_validated_object();
 		*r_ret = a != b;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		const ObjectID &a = VariantInternal::get_object_id(left);
-		const ObjectID &b = VariantInternal::get_object_id(right);
+		Object *a = left->get_validated_object();
+		Object *b = right->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = a != b;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {
@@ -638,12 +638,12 @@ public:
 class OperatorEvaluatorNotEqualObjectNil {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		Object *a = p_left.operator Object *();
+		Object *a = p_left.get_validated_object();
 		*r_ret = a != nullptr;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		Object *a = left->operator Object *();
+		Object *a = left->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = a != nullptr;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {
@@ -655,12 +655,12 @@ public:
 class OperatorEvaluatorNotEqualNilObject {
 public:
 	static void evaluate(const Variant &p_left, const Variant &p_right, Variant *r_ret, bool &r_valid) {
-		Object *b = p_right.operator Object *();
+		Object *b = p_right.get_validated_object();
 		*r_ret = nullptr != b;
 		r_valid = true;
 	}
 	static inline void validated_evaluate(const Variant *left, const Variant *right, Variant *r_ret) {
-		Object *b = right->operator Object *();
+		Object *b = right->get_validated_object();
 		*VariantGetInternalPtr<bool>::get_ptr(r_ret) = nullptr != b;
 	}
 	static void ptr_evaluate(const void *left, const void *right, void *r_ret) {