Untangle remains of MapComponent

[moonheart08]

MapSystem, MapManager, and MapComponent are almost in a state where maps can be treated as true entities.

• Refactor map creation so that maps are normal entities and can be constructed from prototypes.
  This is probably a "just try it and see" moment with a small amount of untangling to do, it looks like it should almost work or just work.
• Make use of CommandBuffers #6461 + EntityBuilders to deprecate the map creation and deletion methods in favor of standard ECS methods.`
• The hard part, deprecate and remove MapId in favor of an all entities house. This may not be necessary, but is a consistency boon.

[moonheart08]

First point is addressed by #6461, trying it and seeing revealed it gets caught on an old assert and then just works.