Docs: Add a @since note for the rest_namespace argument of register_post_type() and register_taxonomy().

Use 3-digit, x.x.x-style semantic versioning for `@since` tags of the `$rest_namespace` property in `WP_Post_Type` and `WP_Taxonomy`.

Add a `@since` note to `WP_REST_Taxonomies_Controller::get_item_schema()` for the `visibility` and `rest_namespace` properties.

The `rest_base` property was also added after the method was initially introduced, but that happened during the same release cycle, so it doesn't need a separate `@since` note.

Follow-up to [38832], [39191], [42729], [51959], [51961], [51962], [51964].

See #53399.

git-svn-id: https://develop.svn.wordpress.org/trunk@51965 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-taxonomy.php

@@ -202,7 +202,7 @@ final class WP_Taxonomy {
 	/**
 	 * The namespace for this taxonomy's REST API endpoints.
 	 *
-	 * @since 5.9
+	 * @since 5.9.0
 	 * @var string|bool $rest_namespace
 	 */
 	public $rest_namespace;