Code Modernization: Explicitly declare all properties in Services_JSON.

Dynamic (non-explicitly declared) properties are deprecated as of PHP 8.2 and are expected to become a fatal error in PHP 9.0.

There are a number of ways to mitigate this:
* If it is an accidental typo for a declared property: fix the typo.
* For known properties: declare them on the class.
* For unknown properties: add the magic `__get()`, `__set()`, et al. methods to the class or let the class extend `stdClass` which has highly optimized versions of these magic methods built in.
* For unknown ''use'' of dynamic properties, the `#[AllowDynamicProperties]` attribute can be added to the class. The attribute will automatically be inherited by child classes.

In this case, the `$use` property, as set in the class constructor, falls in the “known property” category.

Reference: [https://wiki.php.net/rfc/deprecate_dynamic_properties PHP RFC: Deprecate dynamic properties].

Follow-up to [11875], [53557], [53558], [53850], [53851], [53852], [53853], [53854], [53856], [53916], [53935], [53936], [53937], [53938], [53942], [53945], [53948], [53949], [53952], [53953], [53954], [53957].

Props jrf, antonvlasenko, costdev.
See #56033.

git-svn-id: https://develop.svn.wordpress.org/trunk@54037 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-json.php

@@ -121,6 +121,13 @@ define('SERVICES_JSON_USE_TO_JSON', 64);
  */
 class Services_JSON
 {
+   /**
+    * Object behavior flags.
+    *
+    * @var int
+    */
+   public $use;
+
    /**
     * constructs a new JSON instance
     *