It appears to be impossible today to set SO_REUSEPORT on a socket. I'd like to do this on macOS in particular to be able to write mDNS related code in Dart.

One approach might be to add a reusePort option (which I suppose would be ignored on Windows platforms) to bind and propogate that through to the various socket impelmentations the way that reuseAddress is. Another approach would be to simply allow Socket consumers to set arbitrary options on their sockets.

Related to #34782