Convert StomachBehavior to a component/system + rejig body namespaces (#5249)

* Convert StomachBehavior to a component/system + rejig body namespaces

* test

* slightly more namespace changes

* remove

* Hello?????

* fuck you github test runner

* reviews

* oobsy!

Content.Server/Body/Components/RespiratorSystem.cs

@@ -0,0 +1,19 @@
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.Body.Components
+{
+    [UsedImplicitly]
+    public class RespiratorSystem : EntitySystem
+    {
+        public override void Update(float frameTime)
+        {
+            base.Update(frameTime);
+
+            foreach (var respirator in EntityManager.EntityQuery<RespiratorComponent>(false))
+            {
+                respirator.Update(frameTime);
+            }
+        }
+    }
+}