Add support for remote filesystems

[shanept]

When registering the stream, there is a third $flags parameter in which you may specify that a filesystem is 'remote'. It would be very useful in testing codebases implemented for accessing remote filesystems as streams, for example an FTP stream.

[shanept]

If it is any help to you...
I am currently working around this in my test code as follows:

$vfs = vfsStream::setup('root');

stream_wrapper_unregister(vfsStream::SCHEME);
stream_wrapper_register(vfsStream::SCHEME, vfsStreamWrapper::class, STREAM_IS_URL);

It's not pretty, but it does what I need.