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.Client/Flash/FlashSystem.cs

@@ -0,0 +1,64 @@
+using Content.Shared.Flash;
+using Robust.Client.Graphics;
+using Robust.Client.Player;
+using Robust.Shared.GameObjects;
+using Robust.Shared.GameStates;
+using Robust.Shared.IoC;
+using Robust.Shared.Timing;
+
+namespace Content.Client.Flash
+{
+    public class FlashSystem : SharedFlashSystem
+    {
+        [Dependency] private readonly IGameTiming _gameTiming = default!;
+        [Dependency] private readonly IPlayerManager _playerManager = default!;
+        [Dependency] private readonly IOverlayManager _overlayManager = default!;
+
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<FlashableComponent, ComponentHandleState>(OnFlashableHandleState);
+        }
+
+        private void OnFlashableHandleState(EntityUid uid, FlashableComponent component, ref ComponentHandleState args)
+        {
+            if (args.Current is not FlashableComponentState state)
+                return;
+
+            // Yes, this code is awful. I'm just porting it to an entity system so don't blame me.
+            if (_playerManager.LocalPlayer != null && _playerManager.LocalPlayer.Session.AttachedEntityUid != uid)
+            {
+                return;
+            }
+
+            if (state.Time == default)
+            {
+                return;
+            }
+
+            // Few things here:
+            // 1. If a shorter duration flash is applied then don't do anything
+            // 2. If the client-side time is later than when the flash should've ended don't do anything
+            var currentTime = _gameTiming.CurTime.TotalSeconds;
+            var newEndTime = state.Time.TotalSeconds + state.Duration;
+            var currentEndTime = component.LastFlash.TotalSeconds + component.Duration;
+
+            if (currentEndTime > newEndTime)
+            {
+                return;
+            }
+
+            if (currentTime > newEndTime)
+            {
+                return;
+            }
+
+            component.LastFlash = state.Time;
+            component.Duration = state.Duration;
+
+            var overlay = _overlayManager.GetOverlay<FlashOverlay>();
+            overlay.ReceiveFlash(component.Duration);
+        }
+    }
+}