require() throws IllegalArgumentException, not IllegalStateException.

Co-authored-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

To address IDEA's responsiveness issues when reading/writing changelog

* Remove effectively duplicating code
* BufferedChannelIterator is properly registered for cancellation as a corresponding segment 
* Undelivered element handlers are registered via extended segment's protocol
    - Index now encodes information whether segment corresponds to a sender or to a receiver

Fixes #3646

Fixes #3673

…3751)

Follow-up to #3742.
That implementation there did work around issue #3673, but did not restore full binary compatibility: the wrong value of `dispatchTimeoutMs` was passed. Given how `runTest` was used in the problematic library, it should not be a problem, but just to be safe and establish the same behavior even in the deep corner cases, we restore the original implementation fully.