Refactor Flammable to be ECS. (#4671)

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

Content.Shared/Temperature/IsHotEvent.cs

@@ -0,0 +1,14 @@
+using Robust.Shared.Analyzers;
+using Robust.Shared.GameObjects;
+
+namespace Content.Shared.Temperature
+{
+    /// <summary>
+    ///     Directed event raised on entities to query whether they're "hot" or not.
+    ///     For example, a lit welder or matchstick would be hot, etc.
+    /// </summary>
+    public class IsHotEvent : EntityEventArgs
+    {
+        public bool IsHot { get; set; } = false;
+    }
+}