Context: How to get an order by its increment id programmatically?
Implementation
https://github.com/magento/magento2/blob/ffea3cd/app/code/Magento/Sales/Model/Order.php#L435-L444
Usages
1. \Magento\Sales\Helper\Guest::loadValidOrder()
2. \Magento\Checkout\Model\Session::getLastRealOrder()
3. \Magento\Authorizenet\Controller\Adminhtml\Authorizenet\Directpost\Payment\Redirect::_returnQuote()
4. \Magento\Authorizenet\Controller\Adminhtml\Authorizenet\Directpost\Payment\Redirect::execute()()
5. \Magento\Authorizenet\Controller\Adminhtml\Authorizenet\Directpost\Payment\ReturnQuote::_returnQuote()
6. \Magento\Authorizenet\Controller\Directpost\Payment::_returnCustomerQuote()
7. \Magento\Authorizenet\Helper\Backend\Data::getSuccessOrderUrl()
8. \Magento\Authorizenet\Model\Directpost::process()
9. \Magento\Paypal\Block\Iframe::_getOrder()
https://github.com/magento/magento2/blob/ffea3cd/app/code/Magento/Paypal/Block/Iframe.php#L145-L157
10. \Magento\Paypal\Controller\Hostedpro\Redirect::getOrder()
11. \Magento\Paypal\Controller\Payflow\ReturnUrl::execute()
12. \Magento\Paypal\Model\Ipn::_getOrder()
https://github.com/magento/magento2/blob/ffea3cd/app/code/Magento/Paypal/Model/Ipn.php#L129-L143