### 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
return (GDExtensionPtrIndexedSetter)Variant::get_member_ptr_indexed_setter(Variant::Type(p_type));
}
static GDExtensionPtrIndexedGetter gdextension_variant_get_ptr_indexed_getter(GDExtensionVariantType p_type) {
	return (GDExtensionPtrIndexedGetter)Variant::get_member_ptr_indexed_getter(Variant::Type(p_type));
}
static GDExtensionPtrKeyedSetter gdextension_variant_get_ptr_keyed_setter(GDExtensionVariantType p_type) {
	return (GDExtensionPtrKeyedSetter)Variant::get_member_ptr_keyed_setter(Variant::Type(p_type));
}
static GDExtensionPtrKeyedGetter gdextension_variant_get_ptr_keyed_getter(GDExtensionVariantType p_type) {
	return (GDExtensionPtrKeyedGetter)Variant::get_member_ptr_keyed_getter(Variant::Type(p_type));
}
static GDExtensionPtrKeyedChecker gdextension_variant_get_ptr_keyed_checker(GDExtensionVariantType p_type) {
	return (GDExtensionPtrKeyedChecker)Variant::get_member_ptr_keyed_checker(Variant::Type(p_type));
}
static void gdextension_variant_get_constant_value(GDExtensionVariantType p_type, GDExtensionConstStringNamePtr p_constant, GDExtensionUninitializedVariantPtr r_ret) {
	StringName constant = *reinterpret_cast<const StringName *>(p_constant);
	memnew_placement(r_ret, Variant(Variant::get_constant_value(Variant::Type(p_type), constant)));
}
static GDExtensionPtrUtilityFunction gdextension_variant_get_ptr_utility_function(GDExtensionConstStringNamePtr p_function, GDExtensionInt p_hash) {
	StringName function = *reinterpret_cast<const StringName *>(p_function);
	uint32_t hash = Variant::get_utility_function_hash(function);
	if (hash != p_hash) {
		ERR_PRINT_ONCE("Error getting utility function " + function + ", hash mismatch.");
		return nullptr;
	}
	return (GDExtensionPtrUtilityFunction)Variant::get_ptr_utility_function(function);
}
static void gdextension_string_new_with_latin1_chars(GDExtensionUninitializedStringPtr r_dest, const char *p_contents) {