### Godot version

4.0.2.stable.official.7a0977ce2

### System information

Linux

### Issue description

The following code fails with godot-cpp
```c++
Variant variant_int = 1234;
double double_value = variant_int;
UtilityFunctions::print(double_value); // prints 0. it must be 1234

Variant double_variant = 6789.0;
int int_value = double_variant;
UtilityFunctions::print(int_value); // prints 0. it must be 1234

Variant variant_string = "12345";
StringName string_name = variant_string;
UtilityFunctions::print(string_name); // Segmentation Fault!
```

When godot-cpp converts a `Variant` to another type, it calls `type_from_variant_constructor` without checking its type. It only does  `reinterpret_cast` and does no type conversion.
I think this issue can be solved by implementing type conversion on the godot-cpp side or by making `type_from_variant_constructor` do the type conversion.

### Steps to reproduce

Unzip the minimal reproduction project and run `scons` to build the GDExtension.

### Minimal reproduction project

[variant-conversion-issue.zip](https://github.com/godotengine/godot/files/11171860/variant-conversion-issue.zip)

memnew_placement(v->_data._mem, String);
		v->type = Variant::STRING;
	}
	_FORCE_INLINE_ static void init_transform2d(Variant *v) {
		v->_data._transform2d = (Transform2D *)Variant::Pools::_bucket_small.alloc();
		memnew_placement(v->_data._transform2d, Transform2D);
		v->type = Variant::TRANSFORM2D;
	}
	_FORCE_INLINE_ static void init_aabb(Variant *v) {
		v->_data._aabb = (AABB *)Variant::Pools::_bucket_small.alloc();
		memnew_placement(v->_data._aabb, AABB);
		v->type = Variant::AABB;
	}
	_FORCE_INLINE_ static void init_basis(Variant *v) {
		v->_data._basis = (Basis *)Variant::Pools::_bucket_medium.alloc();
		memnew_placement(v->_data._basis, Basis);
		v->type = Variant::BASIS;
	}
	_FORCE_INLINE_ static void init_transform3d(Variant *v) {
		v->_data._transform3d = (Transform3D *)Variant::Pools::_bucket_medium.alloc();
		memnew_placement(v->_data._transform3d, Transform3D);
		v->type = Variant::TRANSFORM3D;
	}
	_FORCE_INLINE_ static void init_projection(Variant *v) {