Fix PayPal Express on events

[MegaphoneJon]

https://lab.civicrm.org/dev/financial/issues/119

Overview

PayPal Express fails on events.

To replicate:

• Set up PayPal Pro.
• Create a paid event using PayPal Pro as the payment processor.
• Attempt to pay via PayPal.

Expected result:

• Payment goes through.

Actual result:
Your browser session has expired and we are unable to complete your form submission. We have returned you to the initial step so you can complete and resubmit the form. If you experience continued difficulties, please contact us for assistance.

Why:
CRM_Event_Form_Registration_Register->postProcess() has these lines:

        $params['component'] = 'event';
        // This code is duplicated multiple places and should be consolidated.
        $params = $this->prepareParamsForPaymentProcessor($params);
        $this->handlePreApproval($params);

But CRM_Core_Form::handlePreApproval() has this line:

      $params['component'] = 'contribute';

As a result, the $params['component'] is ALWAYS treated as contribute, which causes Civi to send the wrong URL to PayPal as the "success URL". so you're redirected back to civicrm/contribute/transact instead of civicrm/event/register.

I have a solution, but I don't have any idea how one tests this. You would need to mock up the PayPal API. Also, this amazingly seems to have been a problem back to 4.7alpha1.

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).

[eileenmcnaughton]

@kcristiano do you have any capacity to test this - I'm thinking of merging based on it looking clearly right & then hoping you will test during rc testing

[kcristiano]

@eileenmcnaughton I should be able to in the next few days.

[eileenmcnaughton]

Thanks @kcristiano

[kcristiano]

@eileenmcnaughton I gave this an r-run I could not reproduce the error on the site I have PayPal Pro/Express configured.

It does work with PR applied, so I'd merge.

[seamuslee001]

I'm going to merge based on @kcristiano's review