Server-client EntityUid separation

[ElectroJr]

Engine version 157.0.0 has introduced server-client EntityUid separation. This means that:

• A given EntityUid will no longer refer to the same entity on the server & client.
• As a consequence, EntityUid is not longer networkable: it cannot be sent in networked messages and component states.
• If you need to send an entity id over the network, use the new NetEntity struct:
  • IEntityManager and entity systems have helper methods for converting between EntityUid and NetEntity
  • Automatic component states are able to handle simple EntityUid fields, but collections will have to be handled manually.
  • If converting a NetEntity into a EntityUid while resolving a component state, you should use the EnsureEntity<TComp>() helper method.

This change does make working with networked entity ids more of a hassle, but in the long term this change will allow us to improve the games performance by reworking how entities/components are stored. It is quite likely that the game may be more unstable/buggy for a while. Downstreams should probably hold off on updating the engine for a week or so. If you run into any issues or bugs, contact @ElectroJr (preferably over discord) or @metalgearsloth