Shared subfloor system (#3590)

* Shared subfloor system

Will also cull the broadphase for server a lot.

* Nullable subfloor

* Snapgrid nullable

* Actually use ComponentDependency

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/IgnoredComponents.cs

@@ -6,7 +6,6 @@ namespace Content.Server
         public static string[] List => new [] {
             "ConstructionGhost",
             "IconSmooth",
-            "SubFloorHide",
             "LowWall",
             "ReinforcedWall",
             "InteractionOutline",