Add destructible component threshold triggers (#3080)

* WIP changes

* Fix tests, merge conflict and trigger once behavior

* Update yml

* Change test strings to be consts

* Fix total damage types and classes triggers

* Simplify damage trigger logic, move state to Threshold

* Update outdated code and docs

* Change the name of IBehavior back to IThresholdBehavior

* Change human gibbing to trigger at 400 brute damage

* Change gibbing from brute to blunt damage

* Fix one (1) typo

* Add damage class trigger test

* Add missing nullable enable to thresholds

Content.Server/GameObjects/Components/Destructible/Thresholds/Behaviors/GibBehavior.cs

@@ -0,0 +1,27 @@
+using Content.Server.GameObjects.EntitySystems;
+using Content.Shared.GameObjects.Components.Body;
+using JetBrains.Annotations;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Serialization;
+
+namespace Content.Server.GameObjects.Components.Destructible.Thresholds.Behaviors
+{
+    [UsedImplicitly]
+    public class GibBehavior : IThresholdBehavior
+    {
+        private bool _recursive = true;
+
+        public void ExposeData(ObjectSerializer serializer)
+        {
+            serializer.DataField(ref _recursive, "recursive", true);
+        }
+
+        public void Execute(IEntity owner, DestructibleSystem system)
+        {
+            if (owner.TryGetComponent(out IBody body))
+            {
+                body.Gib(_recursive);
+            }
+        }
+    }
+}