Refactors flashes to ECS, sunglasses protect you from being flashed. (#4579)

* Refactors flashes to ECS, sunglasses protect you from being flashed.

* VV ReadWrite for FlashImmunity Enabled.

* Use cached IEntityLookup.

* Consistent formatting.

* Fix flashbang duration.
Flash duration is a mess.

* Small area flash code cleanup.

* Flashable state is only sent to attached player.

Content.Shared/Flash/SharedFlashSystem.cs

@@ -0,0 +1,24 @@
+using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
+
+namespace Content.Shared.Flash
+{
+    public abstract class SharedFlashSystem : EntitySystem
+    {
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<SharedFlashableComponent, ComponentGetState>(OnFlashableGetState);
+        }
+
+        private void OnFlashableGetState(EntityUid uid, SharedFlashableComponent component, ref ComponentGetState args)
+        {
+            // Only send state to the player attached to the entity.
+            if (args.Player.AttachedEntityUid != uid)
+                return;
+
+            args.State = new FlashableComponentState(component.Duration, component.LastFlash);
+        }
+    }
+}