Split package kit DataReader.cpp

Pull AttributeDataReader and FDDataReader implementations out of
DataReader.cpp into own source files. Thus we can avoid dependencies
(e.g. to fs_attr code) we don't need/want.

src/add-ons/kernel/file_systems/packagefs/Jamfile

@@ -35,6 +35,7 @@ HAIKU_PACKAGE_FS_PACKAGE_READER_SOURCES =
 	DataOutput.cpp
 	DataReader.cpp
 	ErrorOutput.cpp
+	FDDataReader.cpp
 	PackageContentHandler.cpp
 	PackageData.cpp
 	PackageDataReader.cpp