Bug 5278: Log %err_code for "early" request handling errors (#1382)

Bug 5278: Log %err_code for "early" request handling errors (#1382)

Certain "early" request handling errors (e.g., ERR_TOO_BIG,
ERR_UNSUP_REQ, ERR_UNSUP_HTTPVERSION, ERR_PROTOCOL_UNKNOWN, and
ERR_INVALID_URL) are handled with nil ClientHttpRequest::request object.
ErrorState relied on that object to record error type and details, so
%err_code expanded to "-" in the corresponding access.log records.

Now, ErrorState also uses ALE (where available). ALE already handles the
combination of an early error and late HttpRequest (e.g., the fake one
clientReplyContext::createStoreEntry() creates when handling the error).

This minimal fix does not address known problems with ErrorState::detail
and ErrorState::BuildHttpReply(). It also duplicates related xerrno
detailing code. We will address some of these problems shortly,
including the increased code duplication problem.