Use 'new' expression in places where the type is evident for content (#2590)

* Content.Client

* Content.Benchmarks

* Content.IntegrationTests

* Content.Server

* Content.Server.Database

* Content.Shared

* Content.Tests

* Merge fixes

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Server/GameObjects/EntitySystems/Atmos/AtmosDebugOverlaySystem.cs

@@ -30,7 +30,7 @@ namespace Content.Server.GameObjects.EntitySystems.Atmos
         ///     To modify it see <see cref="AddObserver"/> and
         ///     <see cref="RemoveObserver"/>.
         /// </summary>
-        private readonly HashSet<IPlayerSession> _playerObservers = new HashSet<IPlayerSession>();
+        private readonly HashSet<IPlayerSession> _playerObservers = new();
 
         /// <summary>
         ///     Overlay update ticks per second.