UI/AppKit: Implement an autocomplete view for the location bar

Author: https://github.com/trflynn89
Commit: c1fe912bf9
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4156

UI/AppKit/Interface/Autocomplete.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+#include <AK/Vector.h>
+
+#import <Cocoa/Cocoa.h>
+
+@protocol AutocompleteObserver <NSObject>
+
+- (void)onSelectedSuggestion:(String)suggestion;
+
+@end
+
+@interface Autocomplete : NSPopover
+
+- (instancetype)init:(id<AutocompleteObserver>)observer
+     withToolbarItem:(NSToolbarItem*)toolbar_item;
+
+- (void)showWithSuggestions:(Vector<String>)suggestions;
+- (BOOL)close;
+
+- (Optional<String>)selectedSuggestion;
+
+- (BOOL)selectNextSuggestion;
+- (BOOL)selectPreviousSuggestion;
+
+@end