MDL-44613 behat: strftime format in time to timestamp transformation

Modifies the 'string time to timestamp' behat trasformation to use
userdate() instead of date(). The userdate() method is generally used
throught Moodle for constructing formatted date strings and this change
will provide more consistency and prevent any potential behat failures.
Therefore, if the date format is defined in the given trasformation, it
has to be strftime compatible. Example:
'I should see "##tomorrow noon##%A, %d %B %Y, %I:%M %p##"'

lib/tests/behat/behat_transformations.php

@@ -167,8 +167,8 @@ class behat_transformations extends behat_base {
 
         $count = count($timepassed);
         if ($count === 2) {
-            // If timestamp with spcified format, then retrun date.
-            return date($timepassed[1], $timestamp);
+            // If timestamp with specified strftime format, then return formatted date string.
+            return userdate($timestamp, $timepassed[1]);
         } else if ($count === 1) {
             return $timestamp;
         } else {

lib/upgrade.txt

@@ -48,6 +48,9 @@ information provided here is intended especially for developers.
   those fields. This replaces existing functions get_extra_user_fields(), get_extra_user_fields_sql(),
   get_user_field_name(), get_all_user_name_fields(), and user_picture::fields(), which have all been
   deprecated.
+* The behat transformation 'string time to timestamp' no longer supports datetime format. If provided, the format must
+  be strftime compatible. Example:
+    - I should see "##tomorrow noon##%A, %d %B %Y, %I:%M %p##"
 
 === 3.10 ===
 * PHPUnit has been upgraded to 8.5. That comes with a few changes: