Switch to use Jetpack autoloader instead of Composer's autoloader

[danielbitzer]

Changes proposed in this Pull Request:

Because we are going ahead with using a separate Action Scheduler Job Framework package we need to ensure that the latest version of the package is loaded into WordPress. Jetpack Autoloader was built to solve this problem.

Jetpack autoloader is used also broadly by Woo and Automattic e.g. https://github.com/woocommerce/woocommerce/blob/trunk/composer.json#L17

Closes #1956.

How to test the changes in this Pull Request:

1. Checkout branch
2. Run composer install
3. Load a few Facebook plugin admin pages locally

You can also run something like this to check that various classes are loading. (Copied from https://github.com/woocommerce/facebook-for-woocommerce/pull/1919).

var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Locale::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\AJAX::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Handlers\Connection::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Integrations\Integrations::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Product_Categories::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Commerce::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products\Feed::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products\FBCategories::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products\Stock::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products\Sync::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Products\Sync\Background::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\ProductSets\Sync::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Debug\ProfilingLogger::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Debug\ProfilingLoggerProcess::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Utilities\Shipment::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Utilities\Tracker::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Events\Event::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Events\Normalizer::class ) );
var_dump( class_exists( \SkyVerge\WooCommerce\Facebook\Events\AAMSettings::class ) );
var_dump( class_exists( \Automattic\WooCommerce\ActionSchedulerJobFramework\AbstractJob::class ) );

Changelog entry

Dev - Replace composer autoloader with Jetpack autoloader

[haszari]

@danielbitzer - Do you think we should include this in 2.6, or is it ok to hold off until 2.7?

[danielbitzer]

@haszari I'd probably hold off since 2.6 has been RC'd already. There isn't any urgency to make this change before 2.7.

[rawdreeg]

Will close this PR as stale. And open a new PR to close the issue.