Publicize: Adjust how the Connections Post Field is initialised

In order to make it compatible with use on WPCOM we need to adjust how
the Connections Post Field is initialised. This adds a constructor to
handle registering the `rest_init` hook, and adds the WPCOM specific
logic.

projects/packages/publicize/changelog/update-post-connections-field-config

@@ -0,0 +1,4 @@
+Significance: patch
+Type: changed
+
+Adjusted the initialisation logic for the connections field.

projects/packages/publicize/src/class-connections-post-field.php

@@ -33,6 +33,15 @@ class Connections_Post_Field {
 	 */
 	public $memoized_updates = array();
 
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		// Adding on a higher priority to make sure we're the first field registered.
+		// The priority parameter can be removed once we deprecate WPCOM_REST_API_V2_Post_Publicize_Connections_Field
+		add_action( 'rest_api_init', array( $this, 'register_fields' ), 5 );
+	}
+
 	/**
 	 * Registers the jetpack_publicize_connections field. Called
 	 * automatically on `rest_api_init()`.
@@ -490,3 +499,7 @@ private function is_valid_for_context( $schema, $context ) {
 		return empty( $schema['context'] ) || in_array( $context, $schema['context'], true );
 	}
 }
+
+if ( defined( 'IS_WPCOM' ) && IS_WPCOM ) {
+	wpcom_rest_api_v2_load_plugin( 'Automattic\Jetpack\Publicize\Connections_Post_Field' );
+}

projects/packages/publicize/src/class-publicize-setup.php

@@ -34,12 +34,9 @@ public static function on_jetpack_feature_publicize_enabled() {
 
 		if ( ! isset( $publicize_ui ) ) {
 			$publicize_ui = new Publicize_UI();
-
 		}
 
-		// Adding on a higher priority to make sure we're the first field registered.
-		// The priority parameter can be removed once we deprecate WPCOM_REST_API_V2_Post_Publicize_Connections_Field
-		add_action( 'rest_api_init', array( new Connections_Post_Field(), 'register_fields' ), 5 );
+		new Connections_Post_Field();
 		add_action( 'rest_api_init', array( new REST_Controller(), 'register_rest_routes' ) );
 		add_action( 'current_screen', array( static::class, 'init_sharing_limits' ) );