Add an event for payment failures during checkout

Can someone credit tBKoT, lisastreeter, Nigel Cunningham, jsacksick, Jing Qian, mglaman ... I don't have permissions to do that.

jsacksick → credited Jing Qian → .

jsacksick → credited lisastreeter → .

jsacksick → credited mglaman → .

jsacksick → credited Nigel Cunningham → .

jsacksick → credited tBKoT → .

We just need to add a test here and then we should be good. \Drupal\Tests\commerce_payment\FunctionalJavascript\PaymentCheckoutTest::testFailedCheckoutWithOffsiteRedirectGet looks like one place to do this. We'll need a test module to record the event been triggered and store something in state which we can assert against in the test.

Committed, thanks!!

Automatically closed - issue fixed for 2 weeks with no activity.