REST API: Deprecate `WP_REST_Meta_Fields::register_field()`.

This method never worked properly and cannot be fixed due to incompatible method signatures.

Props flixos90, kadamwhite, jnylen0, TimothyBlynJacobs.
Fixes #39959.

Built from https://develop.svn.wordpress.org/trunk@49295


git-svn-id: http://core.svn.wordpress.org/trunk@49057 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/fields/class-wp-rest-meta-fields.php

@@ -48,10 +48,13 @@ abstract class WP_REST_Meta_Fields {
 	 * Registers the meta field.
 	 *
 	 * @since 4.7.0
+	 * @deprecated 5.6.0
 	 *
 	 * @see register_rest_field()
 	 */
 	public function register_field() {
+		_deprecated_function( __METHOD__, '5.6.0' );
+
 		register_rest_field(
 			$this->get_rest_field_type(),
 			'meta',

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-beta1-49294';
+$wp_version = '5.6-beta1-49295';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.