⛱️ Refactoring closing HTTP/2 session

[masaori335]

There are too many paths to close/free Http2ClientSession/Http2ConnectionState. I know this is result of fixing bunch of issues step by step in the past. However, having similar name functions and call them each other doesn't make sense and it making us hard to find bugs.

Notes

• The order of SSN/TXN close hook is a matter (Fix rare SSN/TXN Start/Close Hook misorderings #6364, TS-4507: Fix SSN and TXN hook ordering. #787)
• vc->add_to_keep_alive_queue() call could be pitfall (Crash on Http2ConnectionState::release_stream() #4504 (comment))

TODOs

• Rename Http2ConnectionState::release_stream() because the name doesn't describe what the function does
• Design how to close Http2ClientSession/Http2ConnectionState simply

[maskit]

Removing Http2ConnectionState (moving its functions into H2Ssn/Txn) would make things much easier.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. Marking it stale to flag it for further consideration by the community.

[masaori335]

#7845 covers this.