MDL-79675 enrol_lti: fix client implementation signatures after upgrade

Not strictly required due to contravariance, but nice for readability.

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

@@ -52,10 +52,10 @@ public function __construct(application_registration_repository $appregrepo,
      * Find and return an LTI registration based on its unique {issuer, client_id} tuple.
      *
      * @param string $iss the issuer id.
-     * @param string $clientId the client_id of the registration.
+     * @param string|null $clientId the client_id of the registration.
      * @return LtiRegistration|null The registration object, or null if not found.
      */
-    public function findRegistrationByIssuer($iss, $clientId = null): ?LtiRegistration {
+    public function findRegistrationByIssuer(string $iss, ?string $clientId = null): ?LtiRegistration {
         if (is_null($clientId)) {
             throw new \coding_exception("The param 'clientid' is required. Calling code must either pass in 'client_id' ".
                 "(generated by the platform during registration) or 'id' (found in the initiate login URI created by the tool) ".
@@ -98,10 +98,10 @@ public function findRegistrationByIssuer($iss, $clientId = null): ?LtiRegistrati
      *
      * @param string $iss the issuer id.
      * @param string $deploymentId the deployment id.
-     * @param string $clientId the client_id of the registration.
+     * @param string|null $clientId the client_id of the registration.
      * @return LtiDeployment|null The deployment object or null if not found.
      */
-    public function findDeployment($iss, $deploymentId, $clientId = null): ?LtiDeployment {
+    public function findDeployment(string $iss, string $deploymentId, ?string $clientId = null): ?LtiDeployment {
         if (is_null($clientId)) {
             throw new \coding_exception("Both issuer and client id are required to identify platform registrations ".
                 "and must be included in the 'aud' claim of the message JWT.");

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

@@ -36,7 +36,7 @@ class launch_cache_session implements ICache {
      * @param string $key the launch id.
      * @return array|null the launch data.
      */
-    public function getLaunchData($key): ?array {
+    public function getLaunchData(string $key): ?array {
         global $SESSION;
         if (isset($SESSION->enrol_lti_launch[$key])) {
             return unserialize($SESSION->enrol_lti_launch[$key]);