[http] Further improvements to Envoy crash logging.

[antoniovicente]

Ref: #7300

We have some logging of the active request on crashes under callstacks that have a ScopeTrackerScopeState but those scoped objects are only associated with events under some HCM, UpstreamRequest and timer callstacks. Also, dumped information is fairly limited.

Possible improvements to ScopeTrackerScopeState to increase dump coverage:

• Have the FileEventImpl or network::ConnectionImpl hold a pointer to the ScopeTrackedObject associated with the current H1 request or active H2 connection. Add a ScopeTrackerScopeState to ConnectionImpl::onFileEvent/FileEventImpl that calls the dump method on the active request's ScopeTrackedObject
• Implement a ScopeTrackedObject for H2 connections that dumps basic info about active streams and recent stream/connection level events.

Possible improvements to request dumps:

• LOG endpoints of the downstream and upstream connection
• If in the middle of H1 header parsing, dump info about contents of read buffer (up to a limit, probably only the first buffer slice)