Review callers of HttpChannelState.onIdleTimeout()

[sbordet]

Jetty version(s)
12+

Description
The callers of HttpChannelState.onIdleTimeout() look for 2 data: a Runnable and a boolean.

For example in HttpConnection:

        if (_httpChannel.getRequest() == null)
            return true;
        Runnable task = _httpChannel.onIdleTimeout(timeout);
        ...

This is slightly racy, and HttpChannelState grabs a lock to check the internal state, so it could do the check on the existence of the request within the lock.

Also, there are difference between HTTP/1.1 and HTTP/2: in H1 there is just a check on the request, but in H2 there is a call to isRequestHandled() which may be equivalent, but the logic should be the same.

This issue is about 2 things:

1. Normalizing the logic across all HTTP versions
2. See if possible to return a null task to indicate to the caller to return true, so that we are not forced to make 2 calls to gather the task and the boolean.

[gregw]

Also see #12301