Added a toggle fullscreen button (default F11) (#20272)

* Added a toggle fullscreen button (default F11)

* Removed un-needed comments

* Review Requested Changes

* Fixed Acidental Spacing Change

* bwoink, removed extraneous code

* nothing, litterally

Content.Client/Fullscreen/FullscreenHook.cs

@@ -0,0 +1,43 @@
+using Content.Shared.Input;
+using Robust.Client.Graphics;
+using Robust.Client.Input;
+using Robust.Shared.Input.Binding;
+using Robust.Shared;
+using Robust.Shared.Configuration;
+using Robust.Shared.Players;
+
+namespace Content.Client.Fullscreen;
+public sealed class FullscreenHook
+{
+    [Dependency] private readonly IInputManager _inputManager = default!;
+    [Dependency] private readonly IConfigurationManager _cfg = default!;
+    [Dependency] private readonly ILogManager _logManager = default!;
+    private ISawmill _sawmill = default!;
+
+    public void Initialize()
+    {
+        _inputManager.SetInputCommand(ContentKeyFunctions.ToggleFullscreen, InputCmdHandler.FromDelegate(ToggleFullscreen));
+        _sawmill = _logManager.GetSawmill("fullscreen");
+    }
+
+    private void ToggleFullscreen(ICommonSession? session)
+    {
+        var currentWindowMode = _cfg.GetCVar(CVars.DisplayWindowMode);
+
+        switch (currentWindowMode)
+        {
+            case (int) WindowMode.Windowed:
+                _cfg.SetCVar(CVars.DisplayWindowMode, (int) WindowMode.Fullscreen);
+                _sawmill.Info("Switched to Fullscreen mode");
+                break;
+
+            case (int) WindowMode.Fullscreen:
+                _cfg.SetCVar(CVars.DisplayWindowMode, (int) WindowMode.Windowed);
+                _sawmill.Info("Switched to Windowed mode");
+                break;
+
+            default:
+                throw new InvalidOperationException($"Unexpected WindowMode value: {currentWindowMode}");
+        }
+    }
+}