Add a new QUICEvent type for reporting errors.
This provides a way to report errors that don't occur as a result of
QUICConn.Start, QUICConn.HandleData, or QUICConn.SendSessionTicket.
Fixes#75108
Change-Id: I941371a21f26b940e75287a66d7e0211fc0baab1
Reviewed-on: https://go-review.googlesource.com/c/go/+/719040
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
