Allow for Workbox.js scripts to be loaded from CDN

[westonruter]

As requested on a support forum topic, some sites may want to load the Workbox scripts from a CDN instead of loading them from origin.

This is not currently supported, as seen here:

pwa-wp/wp-includes/components/class-wp-service-worker-configuration-component.php

Lines 55 to 79 in f9fc1cb

	$workbox_dir = sprintf( 'wp-includes/js/workbox-v%s/', PWA_WORKBOX_VERSION );
	$script = '';
	if ( SCRIPT_DEBUG ) {
	$enable_debug_log = defined( 'WP_SERVICE_WORKER_DEBUG_LOG' ) && WP_SERVICE_WORKER_DEBUG_LOG;
	if ( ! $enable_debug_log ) {
	$script .= "self.__WB_DISABLE_DEV_LOGS = true;\n";
	}
	// Load with importScripts() so that source map is available.
	$script .= sprintf(
	"importScripts( %s );\n",
	wp_json_encode( PWA_PLUGIN_URL . $workbox_dir . 'workbox-sw.js' )
	);
	} else {
	// Inline the workbox-sw.js to avoid an additional HTTP request.
	$wbjs = file_get_contents( PWA_PLUGIN_DIR . '/' . $workbox_dir . 'workbox-sw.js' ); // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
	$script .= preg_replace( '://# sourceMappingURL=.+?\.map\s*$:s', '', $wbjs );
	}
	$options = array(
	'debug' => SCRIPT_DEBUG, // When true, the dev builds are loaded. Otherwise, the prod builds are used.
	'modulePathPrefix' => PWA_PLUGIN_URL . $workbox_dir,
	);
	$script .= sprintf( "workbox.setConfig( %s );\n", wp_json_encode( $options ) );

Perhaps this could be supported by allowing $options to be filtered in PHP.

[westonruter]

Eventually this could be achieved by passing the paths through the includes_url() function so that it could be filtered.

[westonruter]

For now, we can just make use of the plugins_url() function so that the plugins_url filter is applied to the Workbox URLs

[pooja-muchandikar]

QA Passed ✅

To cross check this issue registered a new plugin and was able to load the Workbox.js scripts through CDN, as per the URL passed in the code.

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