AK+Everywhere: Convert JSON value serialization to String

This removes the use of StringBuilder::OutputType (which was ByteString,
and only used by the JSON classes). And it removes the StringBuilder
template parameter from the serialization methods; this was only ever
used with StringBuilder, so a template is pretty overkill here.

AK/JsonArray.cpp

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/JsonArray.h>
+#include <AK/JsonArraySerializer.h>
+#include <AK/StringBuilder.h>
+
+namespace AK {
+
+String JsonArray::serialized() const
+{
+    StringBuilder builder;
+    serialize(builder);
+
+    return MUST(builder.to_string());
+}
+
+void JsonArray::serialize(StringBuilder& builder) const
+{
+    auto serializer = MUST(JsonArraySerializer<>::try_create(builder));
+    for_each([&](auto const& value) {
+        MUST(serializer.add(value));
+    });
+    MUST(serializer.finish());
+}
+
+}