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.Client/State/MainMenu.cs

@@ -40,7 +40,7 @@ namespace Content.Client.State
         private bool _isConnecting;
 
         // ReSharper disable once InconsistentNaming
-        private static readonly Regex IPv6Regex = new Regex(@"\[(.*:.*:.*)](?::(\d+))?");
+        private static readonly Regex IPv6Regex = new(@"\[(.*:.*:.*)](?::(\d+))?");
 
         /// <inheritdoc />
         public override void Startup()