Add synchronous management of stored sessions to QUICConn.

This adds QUICStoreSession and QUICResumeSession events,
permitting a QUIC implementation to handle session resumption
as part of its regular event loop processing.

Fixes #63691

Change-Id: I9fe16207cc1986eac084869675bc36e227cbf3f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/536935


LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Marten Seemann <martenseemann@gmail.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>