Scripts/FollowerAI: Some cleanup:

- FollowerAI properly resumes follow after evading.
- Removed duplicated getters from CreatureAI (IsEscorted vs IsEscortNPC), they were used to do the same thing
- FollowerAI properly assists in combat.
- FollowerAI properly despawns if quest is abandoned.
- FollowerAI now supports dynamic respawning for escort NPCs.

src/server/game/Maps/Map.cpp

@@ -2964,7 +2964,7 @@ bool Map::CheckRespawn(RespawnInfo* info)
                     if (!creature->IsAlive())
                         continue;
                     // escort NPCs are allowed to respawn as long as all other instances are already escorting
-                    if (isEscort && creature->IsEscortNPC(true))
+                    if (isEscort && creature->IsEscorted())
                         continue;
                     doDelete = true;
                     break;