Move and rename damage effect to color flash effect (#18263)

* move damage effect to different package

* rename to ColorFlashEffect

* renaming some other things

Content.Shared/Effects/ColorFlashEffectEvent.cs

@@ -0,0 +1,23 @@
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Effects;
+
+/// <summary>
+/// Raised on the server and sent to a client to play the color flash animation.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed class ColorFlashEffectEvent : EntityEventArgs
+{
+    /// <summary>
+    /// Color to play for the flash.
+    /// </summary>
+    public Color Color;
+
+    public List<EntityUid> Entities;
+
+    public ColorFlashEffectEvent(Color color, List<EntityUid> entities)
+    {
+        Color = color;
+        Entities = entities;
+    }
+}