dev/core#2769 use php email validation not hacked qf

Per https://lab.civicrm.org/dev/core/-/issues/2769 we have had problems over the years with
quickform's email validation and we now have a hacked version that is
problematic from a maintenance pov & also doesn't work
with the string I have just encountered: name.-o-.i.10@example.com
(which I am told is valid and which passes the php filter).

We already have an email rule which calls a php native function
which is better maintained than our layers of hacks. This
PR registers our email rule - which overrides the quickform
one. If we merge this we can revert quickform back to
unhacked which will improve debugging
and maintenance (although it's actually bypassed
now with this change)

CRM/Core/Form.php

@@ -347,6 +347,7 @@ public function registerRules() {
       'settingPath',
       'autocomplete',
       'validContact',
+      'email',
     ];
 
     foreach ($rules as $rule) {