DefaultFilenamePolicy.ParamsCoder loses information whether Params's resource ID is file/directory

DefaultFilenamePolicy.ParamsCoder uses simple StringUtf8Coder for encoding/decoding DefaultFilenamePolicy.Params's baseFilename and therefore looses information whether Params.baseFilename resource ID is file or directory.

The result is that it's effectively preventing user to define directory as baseFilename provider when using dynamic destinations because after deserialization it's translated to file.

Solution is easy - use ResourceIdCoder for encoding/decoding.