Refactor MeleeWeaponComponent and related comps to be ECS (#4133)

* move everything to MeleeWeaponSystem

* refactor MeleeChemicalInjector

* hypospray and flash refactor

* stunbaton refactor

* bugfixes

* flash afterinteract

* resolve issues

* props

* playing the slots

* MeleeInteractEvent + bugfixes

* spear can actually use MeleeChemicalInjector

Content.Server/GameObjects/EntitySystems/ItemCooldownSystem.cs

@@ -0,0 +1,34 @@
+using System;
+using Content.Shared.GameObjects.Components.Items;
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.GameObjects.EntitySystems
+{
+    public class ItemCooldownSystem : EntitySystem
+    {
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<ItemCooldownComponent, RefreshItemCooldownEvent>(OnItemCooldownRefreshed);
+        }
+
+        public void OnItemCooldownRefreshed(EntityUid uid, ItemCooldownComponent comp, RefreshItemCooldownEvent args)
+        {
+            comp.CooldownStart = args.LastAttackTime;
+            comp.CooldownEnd = args.CooldownEnd;
+        }
+    }
+
+    public class RefreshItemCooldownEvent : EntityEventArgs
+    {
+        public TimeSpan LastAttackTime { get; }
+        public TimeSpan CooldownEnd { get;  }
+
+        public RefreshItemCooldownEvent(TimeSpan lastAttackTime, TimeSpan cooldownEnd)
+        {
+            LastAttackTime = lastAttackTime;
+            CooldownEnd = cooldownEnd;
+        }
+    }
+}