StreamInfo: split between downstream and upstream

Currently [StreamInfo](https://github.com/envoyproxy/envoy/blob/main/envoy/stream_info/stream_info.h) is a grab bag for fields that might not make sense for both upstream and downstream (and for that matter for all the places it is used HTTP streams, TCP connections, etc).

Consider splitting in a way that would reduce scope of the interface and make it easier to understand what a particular StreamInfo object is describing.