Add UsedImplicitly to visualizers and entity systems (#2592)

Content.Client/GameObjects/Components/Singularity/ContainmentFieldComponent.cs

@@ -1,3 +1,4 @@
+using JetBrains.Annotations;
 using Robust.Client.GameObjects;
 using Robust.Client.Interfaces.GameObjects.Components;
 using Robust.Shared.GameObjects;
@@ -5,6 +6,7 @@ using Robust.Shared.Log;
 
 namespace Content.Client.GameObjects.Components.Singularity
 {
+    [UsedImplicitly]
     public class ContainmentFieldComponent : Component
     {
         public override string Name => "Containment Field";

Content.Client/GameObjects/Components/Singularity/EmitterVisualizer.cs

@@ -1,10 +1,12 @@
 using System;
 using Content.Shared.GameObjects.Components.Singularity;
+using JetBrains.Annotations;
 using Robust.Client.GameObjects;
 using Robust.Client.Interfaces.GameObjects.Components;
 
 namespace Content.Client.GameObjects.Components.Singularity
 {
+    [UsedImplicitly]
     public class EmitterVisualizer : AppearanceVisualizer
     {
         private const string OverlayBeam = "emitter-beam";