Feat: add constants for PRE and POST serialize

Author: toofff

src/EventListener/EventPriorities.php

@@ -30,6 +30,8 @@ final class EventPriorities
     const POST_VALIDATE = 63;
     const PRE_WRITE = 33;
     const POST_WRITE = 31;
+    const PRE_SERIALIZE = 17;
+    const POST_SERIALIZE = 15;
     const PRE_RESPOND = 9;
     // kernel.response
     const POST_RESPOND = 0;

tests/EventListener/EventPrioritiesTest.php

@@ -31,6 +31,8 @@ public function testConstants()
         $this->assertEquals(63, EventPriorities::POST_VALIDATE);
         $this->assertEquals(33, EventPriorities::PRE_WRITE);
         $this->assertEquals(31, EventPriorities::POST_WRITE);
+        $this->assertEquals(17, EventPriorities::PRE_SERIALIZE);
+        $this->assertEquals(15, EventPriorities::POST_SERIALIZE);
         $this->assertEquals(9, EventPriorities::PRE_RESPOND);
         $this->assertEquals(0, EventPriorities::POST_RESPOND);
     }