LibIMAP: Add a new IMAP client and support NOOP

A large commit, but sets up the framework for how the IMAP library will
work. Right now only the NOOP command and response is supported.

Userland/Libraries/LibIMAP/Parser.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2021, Kyle Pereira <hey@xylepereira.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/Result.h>
+#include <LibIMAP/Objects.h>
+
+namespace IMAP {
+class Client;
+
+struct ParseStatus {
+    bool successful;
+    Optional<Response> response;
+};
+
+class Parser {
+public:
+    ParseStatus parse(ByteBuffer&& buffer, bool expecting_tag);
+
+private:
+    // To retain state if parsing is not finished
+    ByteBuffer m_buffer;
+    SolidResponse m_response;
+    unsigned position { 0 };
+    bool m_incomplete { false };
+    bool m_parsing_failed { false };
+
+    bool try_consume(StringView);
+    bool at_end() { return position >= m_buffer.size(); };
+    void parse_response_done();
+    void consume(StringView x);
+    unsigned parse_number();
+    Optional<unsigned> try_parse_number();
+    void parse_untagged();
+    StringView parse_atom();
+    ResponseStatus parse_status();
+    StringView parse_while(Function<bool(u8)> should_consume);
+};
+}