LibCompress: Add a PackBits decoder

This compression scheme was quite popular during the 80's, and we can
still find it in use inside file formats such as TIFF or PDF.

Userland/Libraries/LibCompress/PackBitsDecoder.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2023, Lucas Chollet <lucas.chollet@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/Optional.h>
+
+namespace Compress::PackBits {
+
+// This implements the PackBits compression scheme, aka run-length compression
+// It is fairly simple and described here: https://web.archive.org/web/20080705155158/http://developer.apple.com/technotes/tn/tn1023.html
+// But also in section:
+//  - 7.4.5 RunLengthDecode Filter of the PDF specification
+//  - Section 9: PackBits Compression of the TIFF specification
+
+enum class CompatibilityMode {
+    Original, // 128 is defined as no-op
+    PDF,      // 128 is defined as end of stream
+};
+
+ErrorOr<ByteBuffer> decode_all(ReadonlyBytes bytes, Optional<u64> expected_output_size = {}, CompatibilityMode mode = CompatibilityMode::Original);
+
+}