Scripts/Instances: Complete rewrite of the boundary system.

- Migrate boundary logic to Maps/AreaBoundary instead of having it sit in InstanceScript (to possibly allow use for other purposes).
- Implement the first five boundary types in Maps/AreaBoundary.cpp.
- Add boundary checks to Creature's update logic
- Add boundary data for all Northrend raids
- Add boundary initialization structures and methods to InstanceScript
- Modify EnterEvadeMode signature. It now passes a value from the EvadeReason enum as parameter to allow special casing depending on evade reason
- Remove previous (weird) boundary code that had them linked to GO spawns

src/server/scripts/Pet/pet_mage.cpp

@@ -167,7 +167,7 @@ class npc_pet_mage_mirror_image : public CreatureScript
                     events.ScheduleEvent(SPELL_MAGE_FIRE_BLAST, TIMER_MIRROR_IMAGE_FIRE_BLAST);
                 }
                 else
-                    EnterEvadeMode();
+                    EnterEvadeMode(EVADE_REASON_OTHER);
             }
 
             void Reset() override
@@ -233,7 +233,7 @@ class npc_pet_mage_mirror_image : public CreatureScript
             }
 
             // Do not reload Creature templates on evade mode enter - prevent visual lost
-            void EnterEvadeMode() override
+            void EnterEvadeMode(EvadeReason /*why*/) override
             {
                 if (me->IsInEvadeMode() || !me->IsAlive())
                     return;