Adds portable flasher (#4523)

Co-authored-by: Paul Ritter <ritter.paul1@googlemail.com>
Co-authored-by: metalgearsloth <comedian_vs_clown@hotmail.com>
Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Server/Explosion/Components/TriggerOnProximityComponent.cs

@@ -0,0 +1,64 @@
+using Content.Server.Explosion.EntitySystems;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Physics.Collision.Shapes;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Robust.Shared.ViewVariables;
+using System.Collections.Generic;
+
+namespace Content.Server.Explosion.Components
+{
+
+    /// <summary>
+    /// Raises a <see cref="TriggerEvent"/> whenever an entity collides with a fixture attached to the owner of this component.
+    /// </summary>
+    [RegisterComponent]
+    public sealed class TriggerOnProximityComponent : Component
+    {
+        public const string FixtureID  = "trigger-on-proximity-fixture";
+
+        public HashSet<PhysicsComponent> Colliding = new();
+
+        [DataField("shape", required: true)]
+        public IPhysShape Shape { get; set; } = new PhysShapeCircle {Radius = 2};
+
+        /// <summary>
+        /// How long the the proximity trigger animation plays for.
+        /// </summary>
+        [ViewVariables]
+        [DataField("animationDuration")]
+        public float AnimationDuration = 0.3f;
+
+        /// <summary>
+        /// Whether the entity needs to be anchored for the proximity to work.
+        /// </summary>
+        [ViewVariables]
+        [DataField("requiresAnchored")]
+        public bool RequiresAnchored { get; set; } = true;
+
+        [ViewVariables]
+        [DataField("enabled")]
+        public bool Enabled = true;
+
+        [ViewVariables(VVAccess.ReadWrite)]
+        [DataField("cooldown")]
+        public float Cooldown { get; set; } = 5f;
+
+        /// <summary>
+        /// How much cooldown has elapsed (if relevant).
+        /// </summary>
+        public float Accumulator = 0f;
+
+        /// <summary>
+        /// What speed should the other object be moving at to trigger the proximity fixture?
+        /// </summary>
+        [ViewVariables(VVAccess.ReadWrite)]
+        [DataField("triggerSpeed")]
+        public float TriggerSpeed { get; set; } = 3.5f;
+
+        /// <summary>
+        /// If this proximity is triggered should we continually repeat it?
+        /// </summary>
+        [DataField("repeating")]
+        internal bool Repeating = true;
+    }
+}