### 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
* @param p_self A pointer to the Variant.
 *
 * @return The boolean value of the Variant.
 */
typedef GDExtensionBool (*GDExtensionInterfaceVariantBooleanize)(GDExtensionConstVariantPtr p_self);
/**
 * @name variant_duplicate
 * @since 4.1
 *
 * Duplicates a Variant.
 *
 * @param p_self A pointer to the Variant.
 * @param r_ret A pointer to a Variant to store the duplicated value.
 * @param p_deep Whether or not to duplicate deeply (when supported by the Variant type).
 */
typedef void (*GDExtensionInterfaceVariantDuplicate)(GDExtensionConstVariantPtr p_self, GDExtensionVariantPtr r_ret, GDExtensionBool p_deep);
/**
 * @name variant_stringify
 * @since 4.1
 *
 * Converts a Variant to a string.
 *
 * @param p_self A pointer to the Variant.
 * @param r_ret A pointer to a String to store the resulting value.
 */
typedef void (*GDExtensionInterfaceVariantStringify)(GDExtensionConstVariantPtr p_self, GDExtensionStringPtr r_ret);
/**
 * @name variant_get_type
 * @since 4.1
 *