Ladybird: Add an AppKit NSString category to hold common utilities

This currently holds a helper to create a new string which collapses all
consecutive whitespace to a single ASCII space.

Ladybird/AppKit/Utilities/NSString+Ladybird.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#import <System/Cocoa.h>
+
+@interface NSString (Ladybird)
+
+- (NSString*)stringByCollapsingConsecutiveWhitespace;
+
+@end

Ladybird/AppKit/Utilities/NSString+Ladybird.mm

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/CharacterTypes.h>
+#include <AK/StringView.h>
+#include <AK/Utf8View.h>
+#include <LibUnicode/CharacterTypes.h>
+
+#import <Utilities/Conversions.h>
+#import <Utilities/NSString+Ladybird.h>
+
+static BOOL code_point_is_whitespace(u32 code_point)
+{
+    static auto white_space_category = Unicode::property_from_string("White_Space"sv);
+
+    if (!white_space_category.has_value())
+        return is_ascii_space(code_point);
+
+    return Unicode::code_point_has_property(code_point, *white_space_category);
+}
+
+@implementation NSString (Ladybird)
+
+- (NSString*)stringByCollapsingConsecutiveWhitespace
+{
+    auto* result = [NSMutableString string];
+
+    auto const* string = [self UTF8String];
+    Utf8View code_points { StringView { string, strlen(string) } };
+
+    bool currently_skipping_spaces = false;
+
+    for (auto code_point : code_points) {
+        if (code_point_is_whitespace(code_point)) {
+            if (!currently_skipping_spaces) {
+                currently_skipping_spaces = true;
+                [result appendString:@" "];
+            }
+
+            continue;
+        }
+
+        auto code_point_string = String::from_code_point(code_point);
+        [result appendString:Ladybird::string_to_ns_string(code_point_string)];
+
+        currently_skipping_spaces = false;
+    }
+
+    return result;
+}
+
+@end

Ladybird/CMakeLists.txt

@@ -142,10 +142,11 @@ elseif (APPLE)
         AppKit/UI/Tab.mm
         AppKit/UI/TabController.mm
         AppKit/Utilities/Conversions.mm
+        AppKit/Utilities/NSString+Ladybird.mm
         AppKit/Utilities/URL.mm
     )
     target_include_directories(ladybird PRIVATE AppKit)
-    target_link_libraries(ladybird PRIVATE ${COCOA_LIBRARY})
+    target_link_libraries(ladybird PRIVATE ${COCOA_LIBRARY} LibUnicode)
     target_compile_options(ladybird PRIVATE
         -fobjc-arc
         -Wno-deprecated-anon-enum-enum-conversion # Required for CGImageCreate