[GDExtension] Cannot convert Variant to other types correctly

[Pylgos]

Godot version

4.0.2.stable.official.7a0977ce2

System information

Linux

Issue description

The following code fails with godot-cpp

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