Refactor Barotrauma to be ECS. (#4674)

- Refactor IPressureProtection to be two different ECS events.

Content.Server/Atmos/PressureEvent.cs

@@ -0,0 +1,46 @@
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.Atmos
+{
+    public abstract class PressureEvent : EntityEventArgs
+    {
+        /// <summary>
+        ///     The environment pressure.
+        /// </summary>
+        public float Pressure { get; }
+
+        /// <summary>
+        ///     The modifier for the apparent pressure.
+        ///     This number will be added to the environment pressure for calculation purposes.
+        ///     It can be negative to reduce the felt pressure, or positive to increase it.
+        /// </summary>
+        /// <remarks>
+        ///     Do not set this directly. Add to it, or subtract from it to modify it.
+        /// </remarks>
+        public float Modifier { get; set; } = 0f;
+
+        /// <summary>
+        ///     The multiplier for the apparent pressure.
+        ///     The environment pressure will be multiplied by this for calculation purposes.
+        /// </summary>
+        /// <remarks>
+        ///     Do not set, add to or subtract from this directly. Multiply this by your multiplier only.
+        /// </remarks>
+        public float Multiplier { get; set; } = 1f;
+
+        protected PressureEvent(float pressure)
+        {
+            Pressure = pressure;
+        }
+    }
+
+    public class LowPressureEvent : PressureEvent
+    {
+        public LowPressureEvent(float pressure) : base(pressure) { }
+    }
+
+    public class HighPressureEvent : PressureEvent
+    {
+        public HighPressureEvent(float pressure) : base(pressure) { }
+    }
+}