Expose internalBinding fs_dir

Is your feature request related to a problem? Please describe.
tschaub/mock-fs#319
mock-fs works through replacing Nodejs internal binding for fs.
We encountered a technical blocker when implementing fs.opendir in mock-fs because the new internalBinding fs_dir is not exposed in process.binding('fs_dir').

Describe the solution you'd like
We would like to suggest to expose fs_dir binding here, so that we could replace it at runtime in mock-fs.

// internalBindingAllowlist contains the name of internalBinding modules
// that are allowed for access via process.binding()... This is used
// to provide a transition path for modules that are being moved over to
// internalBinding.
const internalBindingAllowlist = new SafeSet([
'async_wrap',
'buffer',
'cares_wrap',
'config',
'constants',
'contextify',
'crypto',
'fs',
'fs_event_wrap',
'http_parser',
'icu',
'inspector',
'js_stream',
'natives',
'os',
'pipe_wrap',
'process_wrap',
'signal_wrap',
'spawn_sync',
'stream_wrap',
'tcp_wrap',
'tls_wrap',
'tty_wrap',
'udp_wrap',
'url',
'util',
'uv',
'v8',
'zlib',
]);

Describe alternatives you've considered
N/A