Build/Test Tools: Output a list of discovered routes.

The list of routes to be copied by the `copy:routes` Grunt task is configured dynamically by the `routes:setup` task, which parses the `gutenberg/build/routes/registry.php` file included in the built asset from the `gutenberg` repository.

The task currently produces ouitput only when an error is encountered, such as a missing `registry.php` file or invalide route name.

This adjusts the task to produce output so that the list of routes being processed is clear.

See #65471.

git-svn-id: https://develop.svn.wordpress.org/trunk@62508 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

Gruntfile.js

@@ -2154,6 +2154,14 @@ module.exports = function(grunt) {
 				];
 			} )
 		) );
+
+		grunt.log.writeln(
+			'Found ' + routeNames.length + ' route' + ( routeNames.length === 1 ? '' : 's' ) +
+			' registered in ' + registryPath + ':'
+		);
+		routeNames.forEach( function( name ) {
+			grunt.log.writeln( '  - ' + name );
+		} );
 	} );
 
 	grunt.registerTask( 'build:gutenberg', [