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.

lib/lti1p3/readme_moodle.txt

@@ -4,6 +4,7 @@ This library is a patched for use in Moodle - it requires the following changes
 1. Removal of phpseclib dependency (replaces a single call with openssl equivalent)
 2. Apply the fix from https://github.com/packbackbooks/lti-1-3-php-library/pull/107. If this is already merged upstream, please
 remove this line.
+3. The Packback\Lti1p3\ImsStorage\ImsCookie::setCookie() method has been locally patched to opt-in to Chrome cookie partitioning.
 
 To upgrade to a new version of this library:
 1. Clone the latest version of the upstream library from github:

lib/lti1p3/src/ImsStorage/ImsCookie.php

@@ -2,6 +2,7 @@
 
 namespace Packback\Lti1p3\ImsStorage;
 
+use auth_lti\local\ltiadvantage\utility\cookie_helper;
 use Packback\Lti1p3\Interfaces\ICookie;
 
 class ImsCookie implements ICookie
@@ -33,6 +34,9 @@ class ImsCookie implements ICookie
 
         setcookie($name, $value, array_merge($cookie_options, $same_site_options, $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, $value, array_merge($cookie_options, $options));
     }