Ladybird: Implement a JavaScript console for the AppKit chrome

This adds menu items to open an interactive JavaScript console for a web
page. This more or less mimics the Qt implementation of the console.
Hooks are included to tie the lifetime of the console window with the
tab it belongs to; if the tab is closed, the console window is closed.

Ladybird/AppKit/UI/ConsoleController.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#import <System/Cocoa.h>
+
+@class Tab;
+
+@interface ConsoleController : NSWindowController
+
+- (instancetype)init:(Tab*)tab;
+
+@end