feat(Core/Scripting): Implement OnBeforeCreatureSelectLevel() hook (#17391)

* Add `OnBeforeCreatureSelectLevel()` hook
- allows modules to alter the level of a creature just before it is set

* Fix missing class name.

* Hook should catch even if the level isn't being changed.

* Trim whitespace.

* Revert "Trim whitespace."

This reverts commit 76768d85c0.

* Fix whitespace

src/server/game/Scripting/ScriptDefines/AllCreatureScript.cpp

@@ -48,6 +48,15 @@ void ScriptMgr::OnCreatureSaveToDB(Creature* creature)
     });
 }
 
+void ScriptMgr::OnBeforeCreatureSelectLevel(const CreatureTemplate* cinfo, Creature* creature, uint8& level)
+{
+    ExecuteScript<AllCreatureScript>([&](AllCreatureScript* script)
+    {
+        script->OnBeforeCreatureSelectLevel(cinfo, creature, level);
+    });
+
+}
+
 void ScriptMgr::Creature_SelectLevel(const CreatureTemplate* cinfo, Creature* creature)
 {
     ExecuteScript<AllCreatureScript>([&](AllCreatureScript* script)