curlsecurityblockedhosts does not recognise faß.de as valid domain

Discovered while working on MDL-60279

PHP 7.2 deprecated INTL_IDNA_VARIANT_2003 that we use in admin setting admin_setting_configmixedhostiplist :
https://wiki.php.net/rfc/deprecate-and-remove-intl_idna_variant_2003

cameron1729 and I started looking at the current implementation and Cam noticed that it should be

idn_to_ascii($entry, IDNA_NONTRANSITIONAL_TO_ASCII, INTL_IDNA_VARIANT_UTS46)

because otherwise domains like faß.de would not be converted properly.

While testing we found out that regex in line https://github.com/moodle/moodle/blob/master/lib/tests/admintree_test.php#L154 is incorrect and faß.de does not even pass validation

So there are several problems here:
1. correct regex in ace_encode() so it works with mixed ascii and non-ascii characters
2. change arguments for idn_to_ascii and idn_to_unt8
3. add unittests