LookupServer: Minor overhaul

- Break out request building into a DNSRequest class.
- Break out response parsing into a DNSResponse class.

A DNSRequest contains one or more DNSQuestion objects.
A DNSResponse contains all the DNSQuestions asked, and a DNSAnswer
object for each answer.

Servers/LookupServer/DNSRequest.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include "DNSQuestion.h"
+#include <AK/ByteBuffer.h>
+#include <AK/String.h>
+#include <AK/Types.h>
+
+#define T_A 1
+#define T_NS 2
+#define T_CNAME 5
+#define T_SOA 6
+#define T_PTR 12
+#define T_MX 15
+
+class DNSRequest {
+public:
+    DNSRequest();
+
+    void add_question(const String& name, u16 record_type);
+
+    u16 question_count() const
+    {
+        ASSERT(m_questions.size() < UINT16_MAX);
+        return m_questions.size();
+    }
+
+    u16 id() const { return m_id; }
+    ByteBuffer to_byte_buffer() const;
+
+private:
+    u16 m_id { 0 };
+    Vector<DNSQuestion> m_questions;
+};