### 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 r_ret A pointer to a Variant which will be assigned the value.
 * @param r_valid A pointer to a boolean which will be set to false if the operation is invalid.
 */
typedef void (*GDExtensionInterfaceVariantGetNamed)(GDExtensionConstVariantPtr p_self, GDExtensionConstStringNamePtr p_key, GDExtensionUninitializedVariantPtr r_ret, GDExtensionBool *r_valid);
/**
 * @name variant_get_keyed
 * @since 4.1
 *
 * Gets the value of a keyed property from a Variant.
 *
 * @param p_self A pointer to the Variant.
 * @param p_key A pointer to a Variant representing the key.
 * @param r_ret A pointer to a Variant which will be assigned the value.
 * @param r_valid A pointer to a boolean which will be set to false if the operation is invalid.
 */
typedef void (*GDExtensionInterfaceVariantGetKeyed)(GDExtensionConstVariantPtr p_self, GDExtensionConstVariantPtr p_key, GDExtensionUninitializedVariantPtr r_ret, GDExtensionBool *r_valid);
/**
 * @name variant_get_indexed
 * @since 4.1
 *
 * Gets the value of an index from a Variant.
 *
 * @param p_self A pointer to the Variant.
 * @param p_index The index.
 * @param r_ret A pointer to a Variant which will be assigned the value.
 * @param r_valid A pointer to a boolean which will be set to false if the operation is invalid.
 * @param r_oob A pointer to a boolean which will be set to true if the index is out of bounds.
 */
typedef void (*GDExtensionInterfaceVariantGetIndexed)(GDExtensionConstVariantPtr p_self, GDExtensionInt p_index, GDExtensionUninitializedVariantPtr r_ret, GDExtensionBool *r_valid, GDExtensionBool *r_oob);
/**