MDL-80835 enrol_lti: add partitioning support for OIDC state cookie

Adds the property that is required by Chrome to opt-in to its 3rd party
cookie partitioning solution, CHIPS. This specific change ensures the
'state' cookie, used in the OIDC handshake, has partitioning support.
This cookie can be partitioned unconditionally, since it's a cookie
controlled by the library and one we don't expect to be set without
partitioning elsewhere.

enrol/lti/classes/local/ltiadvantage/lib/lti_cookie.php

@@ -16,6 +16,7 @@
 
 namespace enrol_lti\local\ltiadvantage\lib;
 
+use auth_lti\local\ltiadvantage\utility\cookie_helper;
 use Packback\Lti1p3\Interfaces\ICookie;
 
 /**
@@ -55,6 +56,9 @@ class lti_cookie implements ICookie {
 
         setcookie($name, $value, array_merge($cookieoptions, $samesiteoptions, $options));
 
+        // Necessary, since partitioned can't be set via setcookie yet.
+        cookie_helper::add_attributes_to_cookie_response_header($name, ['Partitioned']);
+
         // Set a second fallback cookie in the event that "SameSite" is not supported.
         setcookie('LEGACY_'.$name, $value, array_merge($cookieoptions, $options));
     }