### Godot version

4.2 247c354

### System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 30.0.15.1403) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

### Issue description

#75778 exposed `_validate_property()` to scripting. It's implemented in GDScript and C#, but not GDExtension (depends on #78634).
https://github.com/godotengine/godot/blob/247c3548d810136ffe9c1694cd76db3236efaa90/core/object/script_language_extension.h#L685-L687

Relevant discussion: https://github.com/godotengine/godot/pull/75778#discussion_r1307294940

### Steps to reproduce

1. Add GDExtension script
2. Use `_validate_property()`

### Minimal reproduction project

N/A
#ifdef TOOLS_ENABLED
	const StringName classname = *reinterpret_cast<const StringName *>(p_classname);
	GDExtensionEditorPlugins::add_extension_class(classname);
#endif
}
static void gdextension_editor_remove_plugin(GDExtensionConstStringNamePtr p_classname) {
#ifdef TOOLS_ENABLED
	const StringName classname = *reinterpret_cast<const StringName *>(p_classname);
	GDExtensionEditorPlugins::remove_extension_class(classname);
#endif
}
#define REGISTER_INTERFACE_FUNC(m_name) GDExtension::register_interface_function(#m_name, (GDExtensionInterfaceFunctionPtr)&gdextension_##m_name)
void gdextension_setup_interface() {
	REGISTER_INTERFACE_FUNC(get_godot_version);
	REGISTER_INTERFACE_FUNC(mem_alloc);
	REGISTER_INTERFACE_FUNC(mem_realloc);
	REGISTER_INTERFACE_FUNC(mem_free);
	REGISTER_INTERFACE_FUNC(print_error);
	REGISTER_INTERFACE_FUNC(print_error_with_message);
	REGISTER_INTERFACE_FUNC(print_warning);
	REGISTER_INTERFACE_FUNC(print_warning_with_message);
	REGISTER_INTERFACE_FUNC(print_script_error);
	REGISTER_INTERFACE_FUNC(print_script_error_with_message);
	REGISTER_INTERFACE_FUNC(get_native_struct_size);
	REGISTER_INTERFACE_FUNC(variant_new_copy);
	REGISTER_INTERFACE_FUNC(variant_new_nil);
	REGISTER_INTERFACE_FUNC(variant_destroy);
	REGISTER_INTERFACE_FUNC(variant_call);
	REGISTER_INTERFACE_FUNC(variant_call_static);
	REGISTER_INTERFACE_FUNC(variant_evaluate);