Refactor Flammable to be ECS. (#4671)

- Refactor IHotItem into IsHotEvent.
- Refactor IFireAct into TileFireEvent.

Content.Server/Atmos/TileFireEvent.cs

@@ -0,0 +1,19 @@
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.Atmos
+{
+    /// <summary>
+    ///     Event raised directed to an entity when it is standing on a tile that's on fire.
+    /// </summary>
+    public class TileFireEvent : EntityEventArgs
+    {
+        public float Temperature { get; }
+        public float Volume { get; }
+
+        public TileFireEvent(float temperature, float volume)
+        {
+            Temperature = temperature;
+            Volume = volume;
+        }
+    }
+}