fs/io/TextFile: split into class FileLineReader and AutoGunzipFileLineReader

Detangle dependencies.

src/io/FileLineReader.hxx

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Copyright The Music Player Daemon Project
+
+#pragma once
+
+#include "LineReader.hxx"
+#include "FileReader.hxx"
+#include "BufferedReader.hxx"
+
+class FileLineReader final : public LineReader {
+	FileReader file_reader;
+	BufferedReader buffered_reader;
+
+public:
+	explicit FileLineReader(Path path_fs)
+		:file_reader(path_fs),
+		 buffered_reader(file_reader) {}
+
+	/* virtual methods from class LineReader */
+	char *ReadLine() override {
+		return buffered_reader.ReadLine();
+	}
+};