Per-map parallax support (#9786)

* Per-map parallax support

* Comments for future sloth

* c

* bet

* Fix exception

* VV support

* Fix parallax

* mem

* weightless sounds

* Gravity stuff

* placeholder coz im too lazy to stash don't @ me son

* decent clouds

* sky

* Fast parallax

* Imagine spelling

* Loicense

* perish

* Fix weightless status

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

Content.Shared/Parallax/SharedParallaxSystem.cs

@@ -0,0 +1,16 @@
+using Robust.Shared.GameStates;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Parallax;
+
+/// <summary>
+/// Handles per-map parallax in sim. Out of sim parallax is handled by ParallaxManager.
+/// </summary>
+public abstract class SharedParallaxSystem: EntitySystem
+{
+    [Serializable, NetSerializable]
+    protected sealed class ParallaxComponentState : ComponentState
+    {
+        public string Parallax = string.Empty;
+    }
+}