Add Layers/Instances/Phasing #253
Description
For instanced dungeons, cutscenes, and potentially random events in the world we need a system where players can be moved to an isolated version of a map where only them and select other players can exist at a time. The game appears to call these "layers", which appears to be not much more than a simple integer check to see who can interact with who. Though it's not quite clear if this system is used for all types of instancing and phasing in the game.
For our own implementation there's a couple paths we could take. The simplest way, while keeping it manageable, would probably be to just clone maps to create instanced versions of them and tell the client they're on the original map, but send the NPCs and players of the cloned version of the map. One other option I'm interested in is to basically create "sub-maps". Every sub-map would be a "layer" and have its own monster and character pool, but they would share the general map information with the main map without cloning anything.
Either way, the goal of this issue is to be able to freely, quickly, and easily move players to instances and manage them, which could ideally be used for all situations where we need such functionality.