ZipFileEncoder.addFile() must support File but not String paths.

[PavelTurk]

Consider the following code:

    IO.File file = MemoryFileSystem().file('temp.html')
      ..writeAsString("123", mode: IO.FileMode.writeOnly, flush: true);

    file.readAsString().then((value) => print(value));

    var encoder = ZipFileEncoder();
    encoder.create(path + "/"+'temp.zip');
    encoder.addFile(file);
    encoder.close();

This code doesn't work:

E/flutter ( 5096): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: FileSystemException: Cannot open file, path = 'temp.html' (OS Error: No such file or directory, errno = 2)
E/flutter ( 5096): #0      _File.throwIfError (dart:io/file_impl.dart:635:7)
E/flutter ( 5096): #1      _File.openSync (dart:io/file_impl.dart:479:5)
E/flutter ( 5096): #2      new FileHandle (package:archive/src/io/input_file_stream.dart:16:25)
E/flutter ( 5096): #3      new InputFileStream (package:archive/src/io/input_file_stream.dart:81:17)
E/flutter ( 5096): #4      ZipFileEncoder.addFile (package:archive/src/io/zip_file_encoder.dart:67:22)

The problem is that in addFile the first line is var fileStream = InputFileStream(file.path);. So, as we see File type is not supported. So, I suggest to add such support.