Core/AI: AreaBoundary refactor

- Added an auxiliary function IsInBounds to base CreatureAI
- Changed container to vector. Set had no sense because we're storing new pointers, they have different addresses even if the boundary is the same

(cherry picked from commit 2f99fa09c9)

src/server/game/Instances/InstanceScript.cpp

@@ -145,7 +145,7 @@ void InstanceScript::LoadBossBoundaries(const BossBoundaryData& data)
 {
     for (BossBoundaryEntry const& entry : data)
         if (entry.BossId < bosses.size())
-            bosses[entry.BossId].boundary.insert(entry.Boundary);
+            bosses[entry.BossId].boundary.push_back(entry.Boundary);
 }
 
 void InstanceScript::LoadMinionData(const MinionData* data)