Change all of body system to use entities and components (#2074)

* Early commit

* Early commit 2

* merging master broke my git

* does anyone even read these

* life is fleeting

* it just works

* this time passing integration tests

* Remove hashset yaml serialization for now

* You got a license for those nullables?

* No examine, no context menu, part and mechanism parenting and visibility

* Fix wrong brain sprite state

* Removing layers was a mistake

* just tear body system a new one and see if it still breathes

* Remove redundant code

* Add that comment back

* Separate damage and body, component states, stomach rework

* Add containers for body parts

* Bring layers back pls

* Fix parts magically changing color

* Reimplement sprite layer visibility

* Fix tests

* Add leg test

* Active legs is gone

Crab rave

* Merge fixes, rename DamageState to CurrentState

* Remove IShowContextMenu and ICanExamine

Content.Shared/GameObjects/Components/Body/Part/Property/ExtensionComponent.cs

@@ -0,0 +1,23 @@
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.GameObjects.Components.Body.Part.Property
+{
+    [RegisterComponent]
+    public class ExtensionComponent : BodyPartPropertyComponent
+    {
+        public override string Name => "Extension";
+
+        /// <summary>
+        ///     Current distance (in tiles).
+        /// </summary>
+        public float Distance { get; set; }
+
+        public override void ExposeData(ObjectSerializer serializer)
+        {
+            base.ExposeData(serializer);
+
+            serializer.DataField(this, e => e.Distance, "distance", 3f);
+        }
+    }
+}