Order cancelled tweaks

Add filters for order cancelled message, change message class from
success to info and allow to be filtered
wp_kses_post for meta display in admin
Fix apigen search
Update class-wc-form-handler.php

Updated as per comments
Fix the SKU search logic so it works with other filters. Closes #5208
Merge pull request #5206 from ChromeOrange/master

Order cancelled tweaks