whisper/whisperv6: initial commit (clone of v5) (#15324)

whisper/whisperv6/api.go

whisper/whisperv6/benchmarks_test.go

whisper/whisperv6/config.go

whisper/whisperv6/doc.go

whisper/whisperv6/envelope.go

whisper/whisperv6/filter.go

whisper/whisperv6/filter_test.go

whisper/whisperv6/gen_criteria_json.go

whisper/whisperv6/gen_message_json.go

whisper/whisperv6/gen_newmessage_json.go

whisper/whisperv6/message.go

whisper/whisperv6/message_test.go

whisper/whisperv6/peer.go

whisper/whisperv6/peer_test.go

whisper/whisperv6/topic.go

whisper/whisperv6/topic_test.go

whisper/whisperv6/whisper.go

whisper/whisperv6/whisper_test.go