Don't cache WP_Term objects in wp_get_object_cache().

The data stored in the cache should be raw database query results, not
`WP_Term` objects (which may be modified by plugins, and may contain additional
properties that shouldn't be cached).

If term relationships caches were handled in `wp_get_object_terms()` - where
a database query takes place - it would be straightforward to cache raw data.
See #34239. Since, in fact, `get_the_terms()` caches the value it gets from
`wp_get_object_terms()`, we need a technique that allows us to get raw data
from a `WP_Term` object. Mirroring `WP_User`, we introduce a `data` property
on term objects, which `get_the_terms()` uses to fetch cacheable term info.

Fixes #34262.

git-svn-id: https://develop.svn.wordpress.org/trunk@35032 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -95,6 +95,15 @@ final class WP_Term {
 	 */
 	public $count = 0;
 
+	/**
+	 * Info about the term, as stored in the database.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 * @var array
+	 */
+	protected $data = array();
+
 	/**
 	 * Stores the term object's sanitization level.
 	 *
@@ -157,6 +166,8 @@ final class WP_Term {
 		foreach ( get_object_vars( $term ) as $key => $value ) {
 			$this->$key = $value;
 		}
+
+		$this->data = sanitize_term( $term, $this->taxonomy, $this->filter );
 	}
 
 	/**
@@ -182,4 +193,20 @@ final class WP_Term {
 	public function to_array() {
 		return get_object_vars( $this );
 	}
+
+	/**
+	 * Getter.
+	 *
+	 * @since 4.4.0
+	 * @access public
+	 *
+	 * @return mixed
+	 */
+	public function __get( $key ) {
+		switch ( $key ) {
+			case 'data' :
+				return sanitize_term( $this->{$key}, $this->data->taxonomy, 'raw' );
+				break;
+		}
+	}
 }