Add class attribute to form

This makes it easier to target the form for theming because otherwise there is no unique identifier for the form.

Now we have a class for the form and wrapper div which is made up of fp- + a sanitized version of the form name (only alphanumeric and -)

Civi/Inlay/FormProcessor.php

@@ -54,6 +54,7 @@ class FormProcessor extends InlayType {
       'submitButtonText' => $this->config['submitButtonText'],
       'webThanksHTML'    => $this->config['webThanksHTML'],
       'publicTitle'      => $this->config['publicTitle'],
+      'formClass'           => 'fp-' . preg_replace('/[^a-z0-9]+/i', '-', $this->config['formProcessor']),
     ];
     // We use the function instead of FormProcessorInstance.get API because this returns the field types as objects.
     // This allows us to call getOptions() when building the field definitions.