we support getting the port of an individual service, all services, and
also just dumping the raw data in a jsonlike format. Also made the
program terminate once it recieves the data.
$ ./xpc --service com.apple.eos.BiometricKit
com.apple.eos.BiometricKit 49238
$ ./xpc --dump
{"Services": {"com.ap.... (this prints everything)
$ ./xpc --list
com.apple.xpc.remote.mobile_obliteration 49242
com.apple.videoprocessingd.encode.remote 49256
...
com.apple.sysdiagnose.stackshot.remote 49248
com.apple.nfcd.relay.control 49258