Content changes for grid splitting (#7645)

Co-authored-by: Vera Aguilera Puerto <gradientvera@outlook.com>

Content.Server/Atmos/TileAtmosphere.cs

@@ -11,6 +11,7 @@ namespace Content.Server.Atmos
     ///     Internal Atmos class that stores data about the atmosphere in a grid.
     ///     You shouldn't use this directly, use <see cref="AtmosphereSystem"/> instead.
     /// </summary>
+    [Friend(typeof(AtmosphereSystem))]
     public sealed class TileAtmosphere : IGasMixtureHolder
     {
         [ViewVariables]