Setup `UpperFloor2` scene

[Girbons]

• Add new child named UpperFloor2 to Environment.tscn scene.
  The structure will be like:

• StaticBody (UpperFloor2)

  • CollisionShape (UpperFloorCollision2)
  • MeshInstance (UpperFloorMesh2)

• Set layer and mask collisions of UpperFloor2 respective as 1 and 2.