Enable landscape for local scene development scenario

[pravusjif]

Problem

When connecting the Explorer to a locally running scene, the landscape should be enabled and dynamically constructed around the parcels used by the scene.

At the moment of writing that's not possible due to the fact that the local scene server Realm (or any Realm that is not a World) doesn't provide any information on the occupied parcels or existent scenes within that realm upon initialization.

In the case of Worlds, the Realm provides a collection of scene URNs, but that is only useful for Worlds, since those scenes are looked up on IPFS, not being the case for a locally running scene or workspace.

Possible strategy

• The sdk-commands Realm logic could be updated to return the local scene parcels used in the "/about" response, when creating the Realm for local scenes, to make that info reach the Explorer when the /About is read.
• Explorer changes needed:
  • When the RealmData is configured by the RealmController (here) the new scenes/parcels collection from the About should be read and passed into the RealmData as "fixed scenes" somehow (e.g.: new collection of Vector2int or scene hashes). realmData.ScenesAreFixed has to end up being true.
  • The LoadFixedPointersSystem.InitiateDefinitionLoading() system query should also check the new scenes collection apart from the sceneUrns collection to load their promises the same way.
  • RealmNavigator.GenerateWorldTerrainAsync() has to be able to read the local scene promise from from the RealmController to be able to actually use the populated parcels to dynamically create the Landscape.

As a helper, keep in mind these scenes loading flow hints: https://excalidraw.com/#json=vHBOS1X8i4UxKxl_ZgC6e,de1hLz3HZpp5J4CJGt8PbQ

[pravusjif]

tackled at https://github.com/decentraland/unity-explorer/pull/2316

[pravusjif]

Already implemented