Merge POST values in confirm-form payment path for tokenized processors.

[emanuel-london]

Overview

Patch to allow new payment processor (Square) extension to work with Webform.

Technical Details

WebformCivicrmConfirmForm::doPayment() does not merge $_POST values into the payment params before calling $paymentProcessor->doPayment(). This means any payment processor that relies on custom POST fields (e.g. tokenized card nonces from Square Web Payments SDK, Stripe payment intents, etc.) will fail with a missing token error when the contribution is routed through the IPN/confirm-form path.
The on-site / live payment path (WebformCivicrmPostProcess::contributionParams()) already merges all POST values into the payment params

// WebformCivicrmPostProcess.php, contributionParams(), ~line 2284
$request = \Drupal::request();
foreach ($request->request->all() as $key => $value) {
  if (empty($params[$key])) {
    $params[$key] = $value;
  }
}

Comments

This affects any payment processor whose doPayment() expects values that are submitted via POST from client-side JavaScript (tokenized/iframe-based processors). Traditional CC processors that use CiviCRM's built-in billing fields are unaffected because those fields are collected by validateBillingFields() and passed through billing_params.